A Simple Device for the On-Site Photodegradation of Pesticide Mixes Remnants to Avoid Environmental Point Pollution

applied sciences

Article A Simple Device for the On-Site Photodegradation of Pesticide Mixes Remnants to Avoid Environmental Point Pollution

Biagio Esposito 1, Francesco Riminucci 1,2 , Stefano Di Marco 3 , Elisa Giorgia Metruccio 3, Fabio Osti 3 , Stefano Sangiorgi 4 and Elida Nora Ferri 4,*

1 Proambiente s.c.r.l.—Tecnopolo Bologna CNR, Via P. Gobetti 101, 40129 Bologna, Italy; [email protected] (B.E.); [email protected] (F.R.) 2 National Research Council, Institute of Marine Sciences (CNR-ISMAR), Via P. Gobetti 101, 40129 Bologna, Italy 3 National Research Council—Institute of BioEconomy (CNR-IBE), Via P. Gobetti 101, 40129 Bologna, Italy; [email protected] (S.D.M.); [email protected] (E.G.M.); [email protected] (F.O.) 4 Department of Pharmacy and Biotechnology, University of Bologna, Via S. Donato 15, 40127 Bologna, Italy; [email protected] * Correspondence: [email protected]; Tel.: +39-0512095658

Featured Application: The prototype developed in this work can rapidly detoxify agrochemical solutions directly at farms, allowing for their safe disposal in the environment or water reuse.

Abstract: The worldwide increase in the number and use of agrochemicals impacts nearby soil and freshwater ecosystems. Beyond the excess in applications and dosages, the inadequate management of remnants and the rinsing water of containers and application equipment worsen this problem, creating point sources of pollution. Advanced oxidation processes (AOPs) such as photocatalytic Citation: Esposito, B.; Riminucci, F.; and photo-oxidation processes have been successfully applied in degrading organic pollutants. Di Marco, S.; Metruccio, E.G.; Osti, F.; We developed a simple prototype to be used at farms for quickly degrading pesticides in water Sangiorgi, S.; Ferri, E.N. A Simple solutions by exploiting a UV–H O -mediated AOP. As representative compounds, we selected the Device for the On-Site 2 2 Photodegradation of Pesticide Mixes insecticide imidacloprid, the herbicide terbuthylazine, and the fungicide azoxystrobin, all in their Remnants to Avoid Environmental commercial formulation. The device efﬁciency was investigated through the disappearance of the Point Pollution. Appl. Sci. 2021, 11, parent molecule and the degree of mineralization. The toxicity of the pesticide solutions, before 3593. https://doi.org/10.3390/ and during the treatment, was assessed by Vibrio ﬁscheri and Pseudokirchneriella subcapitata inhibition app11083593 assays. The results obtained have demonstrated a cost-effective, viable alternative for detoxifying the pesticide solutions before their disposal into the environment, even though the compounds, or Academic Editor: Amerigo Capria their photoproducts, showed different sensitivities to physicochemical degradation. The bioassays revealed changes in the inhibitory effects on the organisms in agreement with the analytical data. Received: 25 March 2021 Accepted: 12 April 2021 Keywords: agrochemicals; photo-reactor; advanced oxidation processes; water pollution; point sources Published: 16 April 2021

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in 1. Introduction published maps and institutional afﬁl- iations. Pesticides, herbicides, fertilizers, plant growth regulators, and other agrochemicals play a decisive role in agriculture, protecting crops and improving yields, but the current main challenge is the development of proﬁt-gaining agriculture increasingly geared to environmentally friendly management systems, aimed at reducing the damages produced by agrochemicals to humans and the environment [1]. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. High intensity agricultural models are characterized by a massive use of pesticides This article is an open access article and herbicides contaminating water and soil [2–4]. In 2018, the worldwide quantities of distributed under the terms and applied pesticides corresponded to 4112.3 metric tons, and in Italy alone to 54.1 metric conditions of the Creative Commons tons [5]. Animal waste from farms, sediments, organic debris, pesticides, and fertilizers Attribution (CC BY) license (https:// have long proven to be the major causes of ground and surface water pollution [6,7]. creativecommons.org/licenses/by/ Soil and water bodies risk contamination every time pesticides are manipulated [8]. 4.0/). Pesticide drift, percolation, drainage, runoff, and leaching greatly depend on their cor-

Appl. Sci. 2021, 11, 3593. https://doi.org/10.3390/app11083593 https://www.mdpi.com/journal/applsci Appl. Sci. 2021, 11, x FOR PEER REVIEW 2 of 17

tons [5]. Animal waste from farms, sediments, organic debris, pesticides, and fertilizers have long proven to be the major causes of ground and surface water pollution [6,7]. Appl. Sci. 2021, 11, 3593 Soil and water bodies risk contamination every time pesticides are manipulated [8].2 of 16 Pesticide drift, percolation, drainage, runoff, and leaching greatly depend on their correct management, both before and after the treatment, including the correct use of the application equipment, i.e., the pneumatic sprayers [9–11]. A known source of point source rect management, both before and after the treatment, including the correct use of the pollution is represented by incorrect practices in the disposal of spray remnants and tank application equipment, i.e., the pneumatic sprayers [9–11]. A known source of point rinsing water. Directive 2009/128/EC [12] regulates the disposal of agro-wastewater con- source pollution is represented by incorrect practices in the disposal of spray remnants and taining pesticides; however, it is quite common for, after the application, the spray rem- tank rinsing water. Directive 2009/128/EC [12] regulates the disposal of agro-wastewater nantscontaining in the barrel pesticides; of the however,spray-tank it to is be quite deposited common on for, the after ground the application,or even discarded the spray directlremnantsy into water in the bodies barrel, of often the spray-tankwithout any to bedilution. deposited These on point the ground sources or of even pollution discarded fromdirectly leftover into mixture water and bodies, cleaning often water without disposal any dilution. are a matter These of concern point sources since pesticide of pollution residuesfrom leftovermay persist mixture for a and very cleaning long time water; some disposal compounds are a matter can be of concernstill detected since many pesticide yearsresidues after their may ban persist [13,14]. for a very long time; some compounds can be still detected many yearsSeveral after solutions their ban have [13 ,been14]. studied and proposed to remove or inactivate pesticides in water.Several Most are solutions plants havebased been on water studied evaporation and proposed produced to remove by solar or inactivate radiation pesticides and windin (Heliosec water. Most® , Syngenta are plants Agro based sas, on Guyancourt, water evaporation France) producedor by infrared by solar radiation radiation and and heatwind (Osmofilm (Heliosec® , Panteck®, Syngenta- France Agro sarl, sas, Montesson Guyancourt, France) France) [15]. or by Quicker infrared evaporation radiation and can heat be obtained(Osmofilm by® using, Panteck- electric Franceal resistance, sarl, Montesson filtering France) the vapors [15]. through Quicker activated evaporation carbon can be filtersobtained (Evapofit by® using, Staphytr, electrical Inchy resistance,-en-Artois, filtering France the) [15]. vapors Otherwise, through a activated chemical carbonpretreat- filters ment(Evapofit of coagulation®, Staphytr,–flocculation Inchy-en-Artois, can be used France) to produce [15]. Otherwise, decantation a chemical of the active pretreatment ingre- of dientcoagulation–flocculation as solid material (Sentinel can be® , Alba used toenvironnement produce decantation sas, Cluny, of the France active) ingredient [15]. Various as solid systemsmaterial are based (Sentinel on ®biomass, Alba environnement beds, based on sas, microbial Cluny, France)degradation [15]. Various(using fungi, systems bacteria, are based actinomycetes,on biomass and beds, viruses) based oninto microbial less toxic degradationforms [1,9,16]. (using However, fungi, all bacteria, these solutions actinomycetes, re- quireand a place viruses) and/or into a lessplant toxic where forms they [1 can,9,16 be]. carried However, out. all these solutions require a place and/orMore effective a plant wheretreatment they systems can be carried are required out. , and the most recent and effective water treatmentMore technologies effective treatment are based systems on advanced are required, oxidation and processes the most recent(AOPs and), a set effective of innovativewater treatment techniques technologies including areUV- basedbased ontechniques advanced, ultrasound, oxidation processes electron (AOPs), beams, γ a set raysof, and innovative plasma techniquesmethods, which including remove UV-based organic techniques, contaminants ultrasound, by mineralization electron beams, [17]. γ Therays, UV treatments and plasma are methods, the easier which and less remove expensive organic ones, contaminants optimized by by the mineralization addition of a [ 17]. photocatalystThe UV treatments or a radical are mediator, the easier such and lessas H expensive2O2, which ones, promotes optimized the radical by the-mediated addition of a degradationphotocatalyst of the or molecules a radical [1 mediator,8–20], according such as Hto2 Othe2, main which steps promotes illustrated the radical-mediated in Scheme 1. degradation of the molecules [18–20], according to the main steps illustrated in Scheme1.

SchemeScheme 1. UV 1. irradiationUV irradiation in the in presence the presence of H2 ofO2H produces2O2 produces the hydroxyl the hydroxyl radicals radicals responsible responsible for for the fragmentationthe fragmentation of the of organic the organic molecules molecules via (a via) radical (a) radical additio additionn to double to double bonds bonds,, (b) hydrogen (b) hydrogen abstractionabstraction,, and and(c) electron (c) electron transfer transfer to the to molecule. the molecule.

ExactlyExactly like likeother other organic organic pollutants, pollutants, agrochemicals agrochemicals can canbe degraded be degraded by light by light irradi- irradi- ation,ation, especially especially by UV by UVlight. light. A huge A huge number number of studies of studies on the on thephotochemistry photochemistry of these of these pollutantspollutants have have been been carried carried out, out, determining determining the thephotodegradation photodegradation kinetics, kinetics, the degr the degra-a- dationdation pathways, pathways, and andthe optimal the optimal conditions conditions such as such the asaddition the addition of oxidants of oxidants and/or and/orcat- alystscatalysts able to ableenhance to enhance the process the process for the formost the recalcitrant most recalcitrant compounds compounds [21–31]. [21 –31]. OurOur research research group group is involved is involved in the in practical the practical application application of AOPs of AOPs for the for remedia- the remedi- tionation of polluted of polluted waters waters to reduce to reduce environmental environmental dispersion dispersion and restore and restore water quality water qualityfor furtherfor furtherreuse [3 reuse2–34]. [ 32Deeply–34]. Deeplyconvinced convinced that the that best the compliance best compliance to ecofriendly to ecofriendly manage- man- mentagement of agro of-wastewater agro-wastewater can be can obtained be obtained offering offering simple, simple, flexible, ﬂexible, cost cost-effective,-effective, and and time-saving solutions, we designed and built up a small, portable device, a photoreactor effective enough in degrading the active ingredients, which is cheap, extremely easy to use in situ, and not time-consuming concerning the abovementioned solutions. We employed UV irradiation in the presence of hydrogen peroxide to reduce the concentration of the agrochemicals, selecting three pesticides that are widely used in our region, each one representing a different family of agrochemicals: insecticides, herbicides, and fungicides. Appl. Sci. 2021, 11, x FOR PEER REVIEW 3 of 17

time-saving solutions, we designed and built up a small, portable device, a photoreactor effective enough in degrading the active ingredients, which is cheap, extremely easy to use in situ, and not time-consuming concerning the abovementioned solutions. We em- Appl. Sci. 2021, 11, 3593 3 of 16 ployed UV irradiation in the presence of hydrogen peroxide to reduce the concentration of the agrochemicals, selecting three pesticides that are widely used in our region, each one representing a different family of agrochemicals: insecticides, herbicides, and fungi- Terbuthylazinecides. Terbuthylazine (TBA), (TBA), used used worldwide worldwide asa as pre-emergence a pre-emergence herbicide herbicide inin corn farm- farming, showsing, shows persistence, persistence, toxicity, toxicity, and and endocrine endocrine disruption disruption effects effects on on wildlife wildlife and and humans humans [35]. Imidacloprid[35]. Imidacloprid insecticide insecticide (IMI), (IMI), today today among among the the top top ten ten agrochemicals agrochemicals worldwide worldwide [36], has[36], been has ascribedbeen ascribed chronic chronic toxicity toxicity to multiple to multiple aquatic aquatic taxa taxa [ 37[37]],, and and negativenegative effects effects on on pollinators [38,39]. Azoxystrobin fungicide (AZO), used since 1996, is very toxic for pollinators [38,39]. Azoxystrobin fungicide (AZO), used since 1996, is very toxic for aquatic aquatic organisms and can lead to long-term adverse effects [40]. We tested our degrada- organisms and can lead to long-term adverse effects [40]. We tested our degradation tion prototype on the same solutions used on the farm for treatment. We employed the prototype on the same solutions used on the farm for treatment. We employed the com- commercial formulation (CFs) of the compounds, which could behave differently with mercialrespect formulation to the pure active (CFs) ingredients of the compounds, because of which the pr couldesence behave of the excipients differently [41], with calcu- respect tolating the pure an average active ingredientsresidual volume because of solution of the presencediluted with of the a suitable excipients volume [41], of calculating water anusually average employed residual to volume rinse the of tank. solution Since diluted a degradation with a procedure suitable volume aims to ofeliminate water usuallythe employedpollutants to’ negative rinse the impact tank. Since on the a degradationenvironment, procedure the success aims of the to eliminateprocedure theis usually pollutants’ negativewitnessed impact by the on reduction the environment, or disappearance the success of the ofir the biotoxicity. procedure We is evaluated usually witnessed the bio- by thetoxicity reduction of irradiated or disappearance and non-irradiated of their biotoxicity.solutions by Weapplying evaluated two ISO the standard biotoxicity biologi- of irradi- atedcal andtests non-irradiatedfor water quality solutions assessment, by applyingbased on Vibrio two ISOfischeri standard light emission biological inhibition tests for and water qualityPseudokirchneriella assessment, subcapitatabased on Vibrio (now ﬁscheriRaphidocelislight emissionsubcapitata inhibition) algal growth and Pseudokirchneriella inhibition, re- subcapitataspectively(now [42,43].Raphidocelis subcapitata) algal growth inhibition, respectively [42,43].

2.2. Materials Materials and and MethodsMethods TheThe commercial commercial formulations formulations of of the the tested tested agrochemicals agrochemicals were: were: TrekP TrekP® (ADAMA® (ADAMA AGAN,AGAN, Ltd., Ltd., Ashdod, Ashdod, Israel) Israel) for for the the herbicide herbicide Terbuthylazine, Terbuthylazine, Conﬁdor Confidor®® (Bayer(Bayer AG, AG, Lev- erkusen,Leverkusen, Germany) Germany) for thefor insecticidethe insecticide Imidacloprid, Imidacloprid, and and Ortiva Ortiva® ®(Syngenta (Syngenta Italia,Italia, Mi- Milano, Italy)lano, for Italy) the for fungicide the fungicide Azoxystrobin. Azoxystrobin. The chemicalThe chemical structure structure of theof the active active ingredients ingredi- is reportedents is reported in Figure in1 .Figure 1.

Figure 1. The chemical structure of the compounds under study: (A) imidacloprid, (B) Figure 1. The chemical structure of the compounds under study: (A) imidacloprid, (B) azoxystrobin, azoxystrobin, and (C) Terbuthylazine. and (C) Terbuthylazine.

® The H2O2 solution (30%) Perhydrol ®, used as a catalyst in the AOP experiments, was suppliedThe H by2O Merck2 solution Life Science (30%) Perhydrol (Milano, Italy)., used The as LCK a catalyst-385 test in-in the-cuvette AOP kit experiments, for the total was suppliedorganic bycompound Merck Life determination Science (Milano, was supplied Italy). The by Hac LCK-385h Lange test-in-cuvette (Milano, Italy). kit Lyophi- for the total organiclized aliquots compound of the determination luminescent bacteria was supplied V. fischeri by Hachwere prepared Lange (Milano, from fr Italy).esh cultures Lyophilized at aliquotsour laboratory of the luminescent starting from bacteria an originalV. fischeri batch suppliedwere prepared by the Pasteur from fresh Institute cultures (Paris, at our laboratoryFrance). The starting 96-wells from “Black an original Cliniplate” batch microplates supplied bywere the supplied Pasteur by Institute Thermo (Paris, Scientific France). The(Vantaa, 96-wells Finland) “Black and Cliniplate” the luminometer microplates was were the Victor supplied Light by 1420 Thermo model Scientific from Perkin (Vantaa,- Finland)Elmer, andUSA. the The luminometer Istituto Zooprofilattico was the Victor Sperimentale Light 1420 of model Abruzzo from and Perkin-Elmer, Molise “G. USA. The Istituto Zooprofilattico Sperimentale of Abruzzo and Molise “G. Caporale” (Teramo, Italy) supplied the freshwater microalga P. subcapitata culture. Inorganic salts and nutrient broth components for the bioluminescent bacteria and algal growth were obtained from Sigma-Aldrich. Tap water was chosen as the solvent of the agrochemicals. A DR5000 spectrophotometer (Hach Lange, Milano, Italy) was employed to evaluate the active ingredients concentration and the total organic compounds (TOC) content. The photoreactor prototype was assembled at the Proambiente laboratories by using materials currently employed in AOP experiments (UV lamps and stainless steel components). Appl. Sci. 2021, 11, 3593 4 of 16

2.1. The Photodegradation Treatment The experiments were planned according to the hypothesis that the residual volume of agrochemical solution in a spray tank after the treatment was about 5 L. Agrochemical solutions were prepared at concentrations very close to the recommended ones employed on ﬁelds. Accordingly, we decided to dissolve 6.25 mL of each pesticide suspension in 5 L of tap water, and then this volume was brought to 50 L, simulating the water volume used during the rinsing operation of an 800 L tank. Before starting the degradation process, 50 mL of H2O2 30% solution was added, obtaining a 10 mM ﬁnal concentration. Small specimens of the solution under treatment (5–10 mL) were collected before the start and after 2, 3, 4, 5, 6, 7, and 8 h after the beginning of the irradiation. The lamps were always switched on during the treatment time. The degradation process was evaluated by following the decrease of the active ingredients’ concentration by measuring their absorbance (ABS) at the maximum wavelength for each compound: 242 nm for TBA and AZO and 270 nm for IMI. The mineralization process was followed by spectrophotometrically measuring the TOC value determined by the Hach Lange test kit. The test was performed according to the manufacturer’s in- structions. Shortly thereafter, the sample was added to the cuvette containing the digestion reagents. After 5 min in the TOC-X5 shaker (Hach Lange, Milano, Italy), a second cuvette containing the revealing reagent was screwed on the digestion cuvette, which was placed in a thermostat for two hours. After cooling at room temperature, the revealing cuvette was read by the spectrophotometer. All experimental results were obtained in at least triplicate and the data were expressed as means ± SD.

2.2. The Toxicity Assays 2.2.1. Bioluminescence Inhibition Assay Lyophilized aliquots of V. ﬁscheri containing NaCl 3% w/v were reconstituted with 1 mL of distilled water and re-suspended in 10–30 mL of the nutrient broth (NaCl 15 g, peptone 2.5 g, yeast extract 1.5 g, glycerol 1.5 mL, HEPES 0.01 M in 500 mL, pH 7). NaCl was added to the treated and untreated solutions to the 3% w/v. 200 µL of the bacteria suspension and 100 µL of each sample was dispensed into the microplate wells. The controls consisted of 200 µL of bacteria plus 100 µL of a 3% NaCl solution in tap water. The emitted light was recorded at ﬁxed intervals in the range 0–48 h. A minimum of 5 replicates and a maximum of 12 were tested for each sample and the light emission values, reported as relative luminescence units (RLU), were expressed as means ± SD. The bioluminescence inhibition percentage (I%) was used to express the toxicity of the samples and calculated according to:

Lblank − Lsample I% = × 100 (1) Lblank where L is the intensity of the light emitted by the sample or by the control (blank).

2.2.2. Algal Growth Inhibition Assay The starter culture of P. subcapitata was prepared by inoculating in Erlenmeyer flasks 1 mL of microalgae suspension per 100 mL of the Jaworski’s culture medium −1 −1 −1 −1 (Ca(NO3)2·4H2O 20 g L ; KH2PO4 12.4 g L ; MgSO4·7H2O 50 g L ; NaHCO3 15.9 g L ; −1 −1 EDTAFeNa and EDTANa2 both at 2.25 g L ;H3BO3 2.48 g L ; [(NH4)6Mo7O24·4H2O] −1 −1 −1 1 g L ; MnCl2·4H2O 1.4 g L , cyanocobalamin, biotin, and thiamine, each one 0.04 g L , −1 −1 NaNO3 80 g L ; NaH2PO4·2H2O 36 g L ). The flasks were stopped by a porous cotton plug and illuminated by a white lamp/red lamp Osram daylight 2 × 36 W plus an Osram Gro-Lux lamp 36 W (8 h light/16 h dark) at room temperature of 20 ◦C. To perform the tests, smaller flasks were filled with equal volumes of the treated or untreated samples, added with the suitable amount of Jaworski’s medium salts and the algal diluted suspension (approximately 105 cells mL−1). The small flasks were kept in the Appl. Sci. 2021, 11, 3593 5 of 16

same conditions as the starter culture. Controls were prepared by adding one volume of the Jaworski’s salts mixture to one volume of algae suspension. We evaluated the algal density by measuring the ABS at 545.6 nm, an indirect method for cell counting also suggested in the ISO 8692/2004 [44]. Aliquots of carefully hand-shaken samples or controls were measured without dilution, in triplicate, and then the aliquots were poured back into the ﬂask.

3. Results 3.1. The Portable Photoreactor Prototype The prototype was assembled at the Proambiente laboratories based on the idea of developing a device effective enough to produce significant detoxification of quite large water solution volumes during a reasonable time period (hours) that is robust and easy to be used anywhere a power supply is available. These characteristics of the system, together with the reduced production costs and the simple procedure, should encourage its regular use any time agro-wastewater has to be managed. To design the irradiating unit (or portable reactor) illustrated in Figure2, we considered the average capacity of the spray tanks to be about 800 L, the average volume of residual solution to be 5 L, and the washing volume for this tank to be about 50 L (data obtained from personal communication with Italian spray machine sellers and users). The simplest solution, taking into account that the unit had to be easily transportable, was to prepare a stainless steel, cylindrical container (Ø 300 cm, high 1.007 cm) capable of holding up to 70 L of liquid. The UV lamps were selected, among those commercially available, according to the dimensions of the container. We employed four immersion, 20 W, low-pressure mercury UV lamps emitting a monochromatic light at λ = 254 nm. The lamps were mounted on a circular support to obtain a uniform distribution of the irradiated light inside the sample volume. The support was completed by adding the electric contacts and was placed inside the system case, whose upper part was hermetically closed by a circular cover blocked by a flange to prevent the escape of UV radiation. In addition, the container was equipped with a circular glass window to check the proper functioning of the lamps and with a drain cock to allow for sampling during the irradiation and emptying at the end of the treatment. To proceed with the photodegradation, the washing water must be transferred inside the prototype. The filling of the prototype with the agrochemical solutions can occur at the spray-tank side using an immersion pump, connected on one side to a tube, capped by a filter, and placed inside the solution into the barrel of the spray-tank. On the other side, it is connected to a tube with an automatic stop dispenser to avoid overfilling the container (Figure3).

3.2. The Photodegradation and Mineralization Proﬁles Of the samples withdrawn from the pesticide solution under treatment, we determined a decrease in both the active ingredient concentration and the degree of mineralization, expressed by the reduction in the ABS and in the TOC value, respectively. The amount of hydrogen peroxide added to the solutions (50 mL of H2O2 at 30% solution) was selected according to our previous experience at the lab scale [33] and the literature data [21]. The pH values of the three solutions after hydrogen peroxide addition were in the range 7.4–7.6, and they were not modiﬁed, because this photodegradation procedure was intended for use at farms where a pH adjustment would be an unusual and unlikely operation. Furthermore, those values were suitable for performing the biotoxicity assays both before and after treatment. Appl. Sci. 2021, 11, 3593 6 of 16 Appl. Sci. 2021, 11, x FOR PEER REVIEW 6 of 17

Appl.Figure Sci. 20 2.21,The 11, x portable FOR PEERFigure photolytic REVIEW 2. The portable cell. From photolytic left to cell. right: From external left to right: aspect external and dimensions aspect and ofdimensions the system of the case, scheme of7 theof 17

UV lamps support,system the support case, scheme inside of the the case UV system.lamps support, Below, the a photo support of inside the completed the case system. lamps’ Below, support. a photo of the completed lamps’ support.

To proceed with the photodegradation, the washing water must be transferred inside the prototype. The filling of the prototype with the agrochemical solutions can occur at the spray-tank side using an immersion pump, connected on one side to a tube, capped by a filter, and placed inside the solution into the barrel of the spray-tank. On the other side, it is connected to a tube with an automatic stop dispenser to avoid overfilling the container (Figure 3).

Figure 3. The vacuum pump system employed to quickly and safely transfer the pesticide solution Figure 3. The vacuum pump system employed to quickly and safely transfer the pesticide solution from the spray-tank, or any other container, to the photodegradation unit. from the spray-tank, or any other container, to the photodegradation unit. 3.2. The Photodegradation and Mineralization Profiles It was out of the scope of this work to follow the photodegradation mechanism by determining Of the samples the kind withdrawn and amount from of the the pesticide photoproducts, solution under ﬁrst of treatment, all because we ourdeter- main mined a decrease in both the active ingredient concentration and the degree of minerali- aim was to develop a more effective device by adapting the UV–H2O2 AOP to the out- of-labzation, conditions expressed by encountered the reduction at farmin the locations.ABS and in On the the TOC other value, hand, respectively. several studies on The amount of hydrogen peroxide added to the solutions (50 mL of H2O2 at 30% so- the photochemistry of the selected compounds were already available in the literature, as lution) was selected according to our previous experience at the lab scale [33] and the mentioned in the Introduction. literature data [21]. The pH values of the three solutions after hydrogen peroxide addition were in the range 7.4–7.6, and they were not modified, because this photodegradation procedure was intended for use at farms where a pH adjustment would be an unusual and unlikely operation. Furthermore, those values were suitable for performing the biotoxicity assays both before and after treatment. It was out of the scope of this work to follow the photodegradation mechanism by determining the kind and amount of the photoproducts, first of all because our main aim was to develop a more effective device by adapting the UV–H2O2 AOP to the out-of-lab conditions encountered at farm locations. On the other hand, several studies on the photochemistry of the selected compounds were already available in the literature, as mentioned in the Introduction. In Figure 4, for each pesticide, the data obtained for the absorbance and the TOC parameters were reported in a double-axis graph in order to compare the trends of the two processes. Two hours was the first sampling interval chosen to evaluate the degradation. At that time, only the reduction in concentration of TBA and IMI and a modest IMI mineralization were measurable. Indeed, the AOPs proceed through complex pathways, starting with the fragmentation of the parental organic molecules, followed by various transformations leading, in optimal conditions, to the production of CO2 and carbonates. The disappearance of the parent compound and the reduction of the organic molecule content can follow completely different kinetics.

Appl. Sci. 2021, 11, 3593 7 of 16

In Figure4, for each pesticide, the data obtained for the absorbance and the TOC parameters were reported in a double-axis graph in order to compare the trends of the two processes. Two hours was the ﬁrst sampling interval chosen to evaluate the degradation. At that time, only the reduction in concentration of TBA and IMI and a modest IMI mineralization were measurable. Indeed, the AOPs proceed through complex pathways, starting with the fragmentation of the parental organic molecules, followed by various transformations leading, in optimal conditions, to the production of CO and carbonates. Appl. Sci. 2021, 11, x FOR PEER REVIEW 2 8 of 17 The disappearance of the parent compound and the reduction of the organic molecule content can follow completely different kinetics.

8 1.2

) 1

- 1 6 0.8 4 0.6 0.4

2 ABS ABS nm) (242 TOC TOC (mgC L 0.2 0 0 0 2 3 4 5 6 7 8 Irradiation Time (hours)

TOC ABS

(a)

40 2.5

) 1 - 30 2 1.5 20 mgC mgC L 1

10 0.5

ABS ABS nm) (270 TOC TOC ( 0 0 0 2 3 4 5 6 7 8 Irradiation Time (hours)

TOC ABS

(b)

18 1.6 16

) 1.4 1 - 14 1.2 12 1 10 0.8 mgC mgC L 8 6 0.6

4 0.4 ABS ABS nm) (242 TOC TOC ( 2 0.2 0 0 0 2 3 4 5 6 7 8 Irradiation Time (hours) TOC (c) Figure 4. The changes in both the active ingredient concentration and in the TOC content over Figure 4. The changes in both the active ingredient concentration and in the TOC content over time time with respect to the untreated solutions (irradiation time 0). (a) TBA, (b) IMI, (c) AZO. with respect to the untreated solutions (irradiation time 0). (a) TBA, (b) IMI, (c) AZO. Concerning the selected pesticides, these differences were particularly evident for the compoundConcerning TBA. This the molecule, selected or pesticides, better its degradation these differences derivatives, were resulted particularly in being evident the for the mostcompound recalcitrant. TBA. TBA This was molecule, degraded or at better 80% after its degradationabout 6 h, but derivatives, the TOC value resulted of the in being solutionthe most was recalcitrant. quite unaffected TBA wasafter degraded8 h of treatment at 80% (Figure after 4a). about 6 h, but the TOC value of the solutionA similar was, quiteand definitely unaffected less after pronounced, 8 h of treatment discrepancy (Figure between4a). the two processes was observed for the insecticide IMI; the parental molecule completely disappeared after 5 h of treatment, while to halve the TOC value, 7 h of irradiation was required (Figure 4b). On the opposite, the two phenomena showed the same trend in the case of AZO. The disappearance of the active ingredient was strictly followed by the reduction of the TOC value, both halved after 3 h of treatment. After this time, the two curves slightly diverged, probably because of the formation of resistant photoproducts (Figure 4c). Appl. Sci. 2021, 11, 3593 8 of 16

A similar, and deﬁnitely less pronounced, discrepancy between the two processes was observed for the insecticide IMI; the parental molecule completely disappeared after 5 h of treatment, while to halve the TOC value, 7 h of irradiation was required (Figure4b). On the opposite, the two phenomena showed the same trend in the case of AZO. The disappearance of the active ingredient was strictly followed by the reduction of the TOC value, both halved after 3 h of treatment. After this time, the two curves slightly diverged, probably because of the formation of resistant photoproducts (Figure4c). Appl. Sci. 2021, 11, x FOR PEERThe REVIEW prototype was able to remove about 80% (mean value) of the active ingredients9 of 17 in

an acceptable time (8 h), which can correspond, for example, to an overnight treatment. The mineralization rate was significantly lower, the mean value being about 44%, but it was known thatThe to obtainprototype the was disappearance able to remove ofabout any 80% organic (mean compoundvalue) of the active is a rather ingredients more difficult task.in an acceptable time (8 h), which can correspond, for example, to an overnight treatment. The mineralization rate was significantly lower, the mean value being about 44%, but it 3.3. The Toxicitywas Assaysknown that to obtain the disappearance of any organic compound is a rather more difficult task. In order to evaluate in depth the efficiency of remediation technologies such as AOP treatments, the3.3. determinationThe Toxicity Assays of the pollutant degradation and of the mineralization rate must be coupledIn toorder various to evaluate biological in depth methodologies the efficiency of remediation in order to technologies determine such the as actual AOP changes in toxicitytreatments, of thethe determination treated materials. of the pollutant Toxicity degradation assessment and is of usually the mineralization performed rate by using a set ofmust tests be based coupled on to simple various organisms biological methodologies living in the in environment order to determine of interest. the actual We applied two ofchanges the most in toxicity used of assays the treated to assess materials. the water Toxicity quality, assessment the bioluminescent is usually performed bacteria by using a set of tests based on simple organisms living in the environment of interest. We Vibrio fisheri, and the freshwater microalga Pseudokirchneriella subcapitata, representing the applied two of the most used assays to assess the water quality, the bioluminescent bac- basic level ofteria heterotrophic Vibrio fisheri, andand the autotrophic freshwater organisms.microalga Pseudokirchneriella subcapitata, representing the basic level of heterotrophic and autotrophic organisms. 3.3.1. The Bacterial Bioluminescence Inhibition Test In Figure3.3.1.5a–c, The we Bacterial reported, Bioluminescence separately forInhibition the three Test compounds, the intensities of the bacterial light emissionIn Figure from 5a–c the, we controlsreported, (blank), separately the for solutions the three treatedcompounds, for 2the h, andintensities those of at the end of thethe treatment bacterial light (8 h). emission from the controls (blank), the solutions treated for 2 h, and those at the end of the treatment (8 h).

1200000 1000000 800000 600000 400000 200000 0

-200000 1 h 6 h 24 h 30 h 50 h Light Light emission(RLU) -400000 Contact time (hours) Blank 2 8

(a) 3500000 3000000

(RLU) 2500000 2000000 1500000

emission 1000000

500000 Light Light 0 1h 5h 20 h 30h 48 h Contact time (hours)

Blank 2 8

(b)

Figure 5. Cont. Appl. Sci. 2021, 11, x FOR PEER REVIEW 10 of 17

Appl. Sci. 2021, 11, 3593 9 of 16 Appl. Sci. 2021, 11, x FOR PEER REVIEW 10 of 17

2500000 2000000 2500000 1500000 2000000 1000000 1500000 500000 1000000 0 500000 0

Light emission Light emission (RLU) 4 h 19 h 24 h 28 h 48 h

Light emission Light emission (RLU) 4 h 19 h 24 h 28 h 48 h Contact time (hours) Contact time (hours)

Blank 2 8 Blank 2 8

Figure 5. Light emission from bacteriaFigure 5.Figure Lightin contact emission 5. Light with from emissionthe bacteria untreated from in contact bacteriasolutions with inthe ( contactblank untreated) and with solutions the the solutions untreated (blank) afterand solutions the 2 solutionsh and (blank) 8 hafter and 2 h and 8 h of irradiation. (a) TBA, (b) IMI, (c) AZO. of irradiation. (a) TBA, (b) IMI, (c) AZO.the solutions after 2 h and 8 h of irradiation. (a) TBA, (b) IMI, (c) AZO. Both solutions of TBA, at 2 and 8 h, reduced the light emission to zero, confirming Both Bothsolutions solutions of TBA,that of TBA,theat 2important and at 2 8 and h, decrease reduced 8 h, reduced in the activelight the lightingredientemission emission concentrationto zero, to zero,confirming was confirming ineffective in re- that thethat important the important decreaseducing decrease in the the toxicity in active the activeof ingredient this compound, ingredient concentration a characteristic concentration was probably ineffective was ineffectivecompletely in re- retained in re- by its ducingducing the toxicity the toxicity of thisphotoproducts. of compound, this compound, a characteristic a characteristic probably probably completely completely retained retained by its by photoproducts.its photoproducts. On the contrary, the sample of IMI collected after 2 h of treatment still completely inhibited the light emission, confirming the solution toxicity, but the sample at the end of On theOn contrary the contrary,, the sample the sample of IMI of collected IMI collected after after2 h of 2 treatment h of treatment still completely still completely the treatment showed no inhibition. The light intensity was practically overlapped with inhibited the light emission, confirming the solution toxicity, but the sample at the end inhibited the light emission,that of confirming the control. Thethe insolutioncomplete toxicity, mineralization but the of thesample solution at didthe notend represent of a prob- the treatmentof the treatment showed showednolem inhibition. of residual no inhibition. Thetoxicity light from Theintensity the light degradation was intensity practically products. waspractically overlapped overlapped with that ofwith the thatcontrol. of the The control. incompleteA The similar incomplete mineralization behavior was mineralization observed of the solution by comparing of the did solution not the representcontrol’s did not emission a representprob- with athose of lem ofproblem residual of toxicity residual fromthe toxicity first the and degradation from last treated the degradation samples products. of the products. AZO solution. Again, the sample after 2 h of treat- A similarA similar behavior behavior mentwas observeddeeply was observedinhibited by comparing the by light comparing emission, the control’s whereas the control’s emission at the end emission with of the those treatment with of those it was possible to observe a reduced, albeit still detectable, toxic effect. the firstof theand first last andtreated last samples treated samplesof the AZO of thesolution. AZO Again, solution. the Again, sample the after sample 2 h of after treat- 2 h of treatment deeply inhibitedIn Figure the light6 we reported, emission, for whereas a direct comparison at the end among of the the treatment three compounds, it was the ment deeply inhibited themean light values emission, of the chronic whereas toxicity, at the i.e. end, the %of of the light treatment emission inhibitionit was pos- produced by all sible possibleto observe to a observe reduced,the a reduced, albeitirradiated stillalbeit solutions detectable still and detectable, ,the toxic untreated effect. toxic samples effect. with respect to the control after 24 h of In FigureIn Figure 6 we6 reported,wecontact reported, forwith a forthe direct bacteria. a direct comparison In comparison this way, among it was among easier the threeto the highlight three compounds, compounds, the effects the of the the H2O2–UV meanmean values values of the of chronic thetreatment chronic toxicity, toxicity,on thei.e. light, the i.e., emission% the of %light ofinhibition lightemission emission over inhibition time. inhibition produced produced by all by all the irradiatedthe irradiated solutions solutions and the and untreated the untreated samples samples with withrespect respect to the to control the control after after24 h of 24 h of contact with the bacteria. In this120 way, it was easier to highlight the effects of the H O –UV contact with the bacteria. In this way, it was easier to highlight the effects of the H2O2–UV2 2 treatmenttreatment on the on light the lightemission emission inhibition100 inhibition over overtime. time. 80

120 60 100 40

80 20 0 60 inhibition, % concentration % 0 2 3 4 5 6 7 8 40 Time of treatment (h) 20 % inhibition % Concentration

0 (a) % inhibition, % concentration % 0 2 3 4 5 6 7 8

Time of treatment (h) % inhibition % Concentration

(a)

Figure 6. Cont. Appl. Sci. 2021, 11, 3593 10 of 16 Appl. Sci. 2021, 11, x FOR PEER REVIEW 11 of 17

140 120 100 80 60 40 20 0 -20 0 2 3 4 5 6 7 8

-40 % inhibition, % concentration % -60 Time of treatment (h)

% Inhibition % Concentration

(b) 120

100

0 0 2 3 4 5 6 7 8 % Inhibition, % % concentration -20 Time of treatment (h)

% inhibition % Concentration

(c)

FigureFigure 6. 6. TheThe inhibition inhibition of light of light emission emission produced produced by the by eight the eightsolutions solutions of each of compound, each compound, in- cludingincluding the the untreated untreated solutions solutions (time (time of oftreatment treatment = 0) =. 0).(a) (TBA,a) TBA, (b) ( bIMI,) IMI, (c) (AZO.c) AZO.

ApartApart from from TBA, for whichwhich inhibitioninhibition never never decreased decreased significantly, significantly, interesting interesting behav- be- haviorsiors can can be observed.be observed. After After 4 h of4 h treatment, of treatment a sudden, a sudden reduction reduction in IMI in toxicityIMI toxicity from from 100% 100%to 6% to occurred. 6% occurred. The negative The negative inhibition inhibition values values produced produced by the lastby the three las samplest three samples indicate indicatethat the that photoproducts the photoproducts slightly stimulateslightly stimulate the wellness the wellness of the bacteria, of the mostbacteria, probably most actingprob- ablyas a acting supplementary as a supplementary carbon source. carbon A significant source. A significant drop in AZO drop toxicity in AZO occurred toxicity after occurred 3 h of aftertreatment 3 h of (fromtreatment 83% at(from 2 h to83% 14%). at 2 Surprisingly,h to 14%). Surprisingl AZO solutionsy, AZO treated solutions for atreated longer for time a longer(5–8 h) time partially (5–8 h) recovered partially theirrecovered toxicity their (39%). toxicity This (39%). result This confirmed result confirmed the partial the toxicity par- tialrepresented toxicity represented in Figure5c, in and Figure we can 5c, hypothesize and we can thathypothesize the photoproducts that the photoproducts obtained at those ob- tainedtimes wereat those more times toxic were than more the previoustoxic than ones. the previous ones.

3.3.2.3.3.2. The The Algal Algal Growth Growth Inhibition Inhibition A Assayssay TheThe effects effects of of the the pesticide pesticide solutions solutions on on the the microalgae microalgae growth growth rate rate appeared, appeared, as ex- as pected,expected, different different from from those those on on bacteria bacteria and and,, inin some some cases cases,, more more complicated complicated to to interpret. interpret. TheThe sensitivity sensitivity of of these these organisms organisms is is surely surely lower lower than than that that of of bioluminescent bioluminescent bacteria bacteria,, andand all all solutions, solutions, treated treated or or not, not, took took the the same, same, quite quite long long,, time time to to influence inﬂuence their their growth growth (Figure(Figure 7).7). At At the the start start of the of the experiment experiment and andstill after still after4 days 4 of days contact, of contact, the optical the density optical indensity the samples in the samples(defined (deﬁnedas the absorbance as the absorbance at 545.6 nm) at 545.6 and nm)the controls and the were controls very were similar. very similar. Stopping the experiment at 72 h, as frequently done, these compounds could Stopping the experiment at 72 h, as frequently done, these compounds could be declared Appl. Sci. 2021Appl., 11, 3593 Sci. 2021, 11, x FOR PEER REVIEW 11 of 16 12 of 17

be declarednontoxic. nontoxic. However, However, after after 6 6days days of of contact, contact, the the controls controls continued continued to to grow, grow, whereas all whereas allthe the samples samples of of IMI IMI and and TBA TBA (Figure (Figure 7a,7a,c) c) produced a variable drop in the microalgae microalgaepopulation. population. The The effect effect of of the the various various IMI IMI sa samplesmples was was practically practically the the same, same, i.e., concen- i.e., concentrationtration independent. independent. On On the the contrary, contrary, the the effe effectscts of of the the herbicide herbicide were were more more specific and speciﬁc anddependent dependent on on its its concentration, concentration, and and this this effect effect was was more more evident evident after 4 days of contact. of contact.It It was not possible to deﬁnedefine aa clearclear toxictoxic effecteffect ofofAZO AZO solutions solutions at at all all times, times, since the since the countscounts of of samples samples and and controls controls were were in thein the same same range range even even after after 6 days 6 days from from the the begin- beginning,ning, indicating indicating this fungicide this fungicide as a not as harmfula not harmful compound compound to these to these organisms. organisms.

0.4 0.35 0.3 0.25 0.2 0.15 ABS (545.6 nm) (545.6 ABS 0.1 0.05 0 01234567 Incubation Time (days) Blank 0 2 3 4 5 6 7 8

(a) 0.4 0.35 0.3 0.25 0.2 0.15

ABS (545.6 nm) (545.6 ABS 0.1 0.05 0 01234567 Incubation Time (day)

Blank 0 2 3 4 5 6 7 8

(b)

Figure 7. Cont. Appl. Sci. 2021Appl., 11, 3593 Sci. 2021, 11, x FOR PEER REVIEW 12 of 16 13 of 17

0.4 0.35 0.3 0.25 0.2 0.15

ABS (545.6 nm) (545.6 ABS 0.1 0.05 0 01234567 Incubation Time (days)

Blank 0 2 3 4 5 6 7 8

(c)

Figure 7. The absorbanceFigure 7. valuesThe absorbance were recorded values for were the microalgae recorded for populations the microalgae in cont populationsact with the various in contact solutions with (0–8) and for the controlthe (blank) various immediately solutions (0–8) after and the forpreparation the control of the (blank) samples–algae immediately mixture after (incubation the preparation time of= 0) the and after 4 and 6 days. (asamples–algae) TBA, (b) IMI, mixture(c) AZO. (incubation time = 0) and after 4 and 6 days. (a) TBA, (b) IMI, (c) AZO.

4. Discussions4. Discussions Nowadays,Nowadays, the general the awareness general aboutawareness the incalculable about the incalculable damages produced damages by produced agro- by ag- chemicals onrochemicals all living beingson all imposesliving beings that weimposes take reasonable that we take precautions reasonable to ensureprecautions that to ensure the storage,that handling, the storage, and handling, disposal ofand these disposal products of these do products not endanger do not further endanger human further human health or thehealth environment. or the environment. Nevertheless, Nevertheless, each crop each requires crop requires various treatments,various treatments, and a and a di- direct consequencerect consequence of any phytosanitary of any phytosanitary treatment treatm is, amongent is, others, among the others, generation the generation of a of a pesticide containingpesticide containing a volume ofa agro-wastewatervolume of agro-wastewater from the remnants from the and remnants rinsing and of therinsing of the treatment machinery.treatment machinery. In most cases, In most the fate cases, of unused the fate tank of unused mixes tank is to bemixes simply is to disposed be simply disposed of on the soilof ofon treatedthe soil fields of treated or at fields the farm or at area, the sincefarm thearea, several since the developed several alternativesdeveloped alternatives to correctlyto treat correctly these waste treat resultsthese waste are expensive results are and ex timepensive (and and space)-consuming, time (and space)-consuming, or the or threat posedthe by threat this action posed is by not this completely action is not understood. completely Efficient, understood. more applicable,Efficient, more and applicable, flexible methodsand flexible are in demand.methods are in demand. To promoteTo the promote degradation the degradation of pollutants of by pollutants the oxidation by the of theoxidation organic of compound the organic is compound a powerfulis solution a powerful actually solution applied actually mainly applied to the treatmentmainly to ofthe wastewaters. treatment of Among wastewaters. the Among various possibilitiesthe various offered possibilities by the advancedoffered byoxidation the advanc processes,ed oxidation we selectedprocesses, one we of selected the one of most usedthe in its most simpler usedand in its possibly simpler cheaper and possibly formulation, cheaper the formulation, UV promoted the UV oxidation promoted oxida- supportedtion by the supported addition by of the hydrogen addition peroxide of hydrogen as the peroxide hydroxyl as radicals’the hydroxyl source, radicals’ in a source, in portable, flexible format. a portable, flexible format. We assembled a photodegradation cell able to contain and treat most parts of the We assembled a photodegradation cell able to contain and treat most parts of the remnant volumes from spraying activities or leftover pesticide waste. The use of this device remnant volumes from spraying activities or leftover pesticide waste. The use of this de- is elementary; it must simply be filled and connected to the electric power. Its size make vice is elementary; it must simply be filled and connected to the electric power. Its size it easily transportable and the costs are really reduced. The cost of purchasing it is in the make it easily transportable and the costs are really reduced. The cost of purchasing it is range of €3000–4000 and the maintenance costs concern the substitution of the exhausted in the range of €3000–4000 and the maintenance costs concern the substitution of the ex- UV lamp, in addition to the electric power consumption. Such costs can be supported hausted UV lamp, in addition to the electric power consumption. Such costs can be sup- by any farm, even one of reduced dimensions, and this device can become a small but ported by any farm, even one of reduced dimensions, and this device can become a small effective facility, located exactly where the wastewater detoxification is required. but effective facility, located exactly where the wastewater detoxification is required. By using the commercial formulation of pesticides with different degrees of suscep- By using the commercial formulation of pesticides with different degrees of suscep- tibility to mineralization, the tap water to prepare the solutions, and the concentrations usually presenttibility in to the mineralization, spray-tank washing the tap volumes,water to prepare we exactly the simulatedsolutions, theand scenario the concentrations occurring atusually farms andpresent planned in the a suitablespray-tank treatment washing time, volumes, long enough we exactly to be effectivesimulated but the scenario no too longoccurring so as to be at practically farms and unacceptable.planned a suitable treatment time, long enough to be effective but The chemicalno too long determination so as to be ofpractically the pollutants’ unacceptable. degradation and of the mineralization rate was coupled to biological evaluations aimed at determining if the degradation actually Appl. Sci. 2021, 11, 3593 13 of 16

resulted in a reduction of the toxic effects on the environment, confirming the effectiveness and usefulness of the device. The disappearance of the active ingredient can have completely different kinetics with respect to the reduction of the organic matter content, that being the sensitivity of the parental compound and of its derivatives to oxidative degradation, as well as their toxicity, which are often completely independent [32–34]. The degradation of the selected compounds began immediately, except for the fungicide, whose concentration was reduced later than 2 h, but mineralization was not appre- ciable before 3 h. After 8 h, the degradation of the active ingredients was very satisfying. Overall, for the test, the mineralization rate was significantly lower and at 8 h, less than 50% mineralization had been attained, as an average value. In particular, the photoproducts of TBA are known to be recalcitrant to mineralization [45,46], and this compound was selected just to simulate the worst working conditions. Additionally, the results obtained for the imidacloprid were in agreement with the literature data reporting the formation of several photoproducts during the degradation process of IMI, mainly the well-known 6-chloronicotinic acid, which slows down the mineralization process [25,47]. Nevertheless, these results can be considered extremely positive, and they already seem to offer useful indications for the correct use of the device as such. Indeed, the photoproducts are often more prone to bio- or phytodegradation than their parent compounds, for which fragmentation promotes the different inherent water remediation processes. It was known that photocatalytic or even more powerful techniques must be applied to obtain exhaustive mineralization processes, but these also increase, in parallel, the costs and/or the skills required to carry out these procedures. Moreover, the complete mineralization of organic pollutants is not always necessary. It is not rare that degradation intermediates show higher biotoxicity than the parental compound [47], suggesting that avoiding the presence of these compounds in the environment (blocking them before they reach soil or water) is the only solution. For example, the toxicity of the fungicide collapses after three hours of treatment, corresponding to a drastic increase in both the degradation and mineralization of the parent compound. However, after four hours, toxicity partially resumes and no longer subsides until the test is complete. It is interesting to note that in precisely the vicinity of the fourth hour and, above all, of the fifth hour, the degradation and mineralization curves of the compound diverge, albeit slightly. It could not be excluded that, from that moment on, a toxic product reluctant to mineralization was formed. The use of the device for AOPs for 3–4 h seems to be preferable both to shorter and longer times (within the limits of what has been tested in this work). On the other hand, Imidacloprid shown still the 100% toxicity at 3 h, changed to less the 10% after 4 h of treatment. Nevertheless, the IMI concentration was not so different among 3 and 4 h and in both cases very low. It is possible to imagine that the photoproduct(s) retaining the toxic effect underwent definitive degradation only at 4 h, whereas the organic content was still high (low mineralization rate). Additionally, in this case seems that the optimal effect of the device takes place in 4 h. The assessment of the post-treatment toxicity by the highly sensitive Vibrio fisheri test revealed that in only one case, the TBA, did treated and untreated solutions show the same inhibition effect. The difficulties encountered in removing this compound, or better, its derivatives, surely represent a serious, but fortunately not so frequent, obstacle in wastewater remediation. A detectable impact of the agrochemical solutions on the freshwater microalgae population was observed only after a rather long contact period (144 h). It must be underlined that, for the most part, this kind of assay collects data for shorter periods (72–96 h). In this case, our samples should be considered as not harmful to these organisms. In conclusion, it is possible to affirm that the overall performance of this first version of the photodegradation portable cell was positive, even though the pollutants’ concentration/pH/H2O2 ratios were not the optimal ones, which can be employed in laboratory studies to maximize the degradation yields. Appl. Sci. 2021, 11, 3593 14 of 16

Further improvements of the prototype are under study, such as the application of an accessory to mix the solution during the treatment and to enhance the homogeneity of the UV rays’ absorbance in the whole volume. The results obtained from the current studies must be conﬁrmed on a wider selection of agrochemicals and on a mixture of different compounds and organic pollutants to ascertain the effectiveness and feasibility of this device in various conditions and indicate the possibility for scaling it for different applications. The use of the studied device could also improve crop management in terms of bioeconomy, thanks to the increased possibility of recovering contaminated washing water for other agronomic uses [48].

Author Contributions: Conceptualization, B.E., F.R., and S.D.M.; methodology, B.E. and F.R.; formal analysis F.R. and F.O.; investigation, B.E., E.N.F., and S.S.; data curation, F.R. and E.G.M.; writing— original draft preparation, E.N.F. and S.D.M.; writing E.N.F., S.D.M., B.E., and F.R.—review and editing F.O., S.D.M., E.N.F., S.S., F.R., and B.E.; project administration, F.R. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Acknowledgments: We express our sincere gratitude to Giorgio Longino for his fundamental contri- bution to the realization of the prototype, for his patience during the discussions on its design, and for his great sense of humor. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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