International Journal of Environmental Research and Public Health Review A Detailed Review Study on Potential Effects of Microplastics and Additives of Concern on Human Health Claudia Campanale * , Carmine Massarelli , Ilaria Savino, Vito Locaputo and Vito Felice Uricchio Water Research Institute-Italian National Research Council (IRSA-CNR), Bari, BA, Italy; [email protected] (C.M.); [email protected] (I.S.); [email protected] (V.L.); [email protected] (V.F.U.) * Correspondence: [email protected] Received: 29 December 2019; Accepted: 7 February 2020; Published: 13 February 2020 Abstract: The distribution and abundance of microplastics into the world are so extensive that many scientists use them as key indicators of the recent and contemporary period defining a new historical epoch: The Plasticene. However, the implications of microplastics are not yet thoroughly understood. There is considerable complexity involved to understand their impact due to different physical–chemical properties that make microplastics multifaceted stressors. If, on the one hand, microplastics carry toxic chemicals in the ecosystems, thus serving as vectors of transport, they are themselves, on the other hand, a cocktail of hazardous chemicals that are added voluntarily during their production as additives to increase polymer properties and prolong their life. To date, there is a considerable lack of knowledge on the major additives of concern that are used in the plastic industry, on their fate once microplastics dispose into the environment, and on their consequent effects on human health when associated with micro and nanoplastics. The present study emphasizes the most toxic and dangerous chemical substances that are contained in all plastic products to describe the effects and implications of these hazardous chemicals on human health, providing a detailed overview of studies that have investigated their abundance on microplastics. In the present work, we conducted a capillary review of the literature on micro and nanoplastic exposure pathways and their potential risk to human health to summarize current knowledge with the intention of better focus future research in this area and fill knowledge gaps. Keywords: microplastics; additives; human health; nanoplastics 1. The Plasticene In the last 70 years, we have abetted an increasing growth in the worldwide plastics production, which has consequently spread into the environment to such a point that we can say to live in a plastic world [1,2]. These synthetic polymers are environmental pollutants themselves and act as vectors of transport of various kind of chemicals [3], but they are also considered valid indicators of the recent and contemporary period, generally after the middle of the 20th century [4]. Nowadays, microplastic particles have been ubiquitously detected in a broad range of shapes, polymers, sizes and concentrations in the environments of marine water, freshwater [5], agroecosystems [6], atmosphere [7], food [8] and drinking-water [9], biota [10], and other remote locations [11]. They can be as thin as small veils and be carried away by the wind from miles away, or they can be hard and compact like rocks [12]. Int. J. Environ. Res. Public Health 2020, 17, 1212; doi:10.3390/ijerph17041212 www.mdpi.com/journal/ijerph Int. J. Environ. Res. Public Health 2020, 17, 1212 2 of 27 Int. J. Environ. Res. Public Health 2020, 17, 1212 2 of 26 Their worldwide distribution is so vast that many scientists use it as a key geological indicator of the Anthropocene [4]. Their worldwidePlastic materials distribution can be used is so as vaststratigraphic that many markers scientists in the archaeological use it as a keyfield geologicalby considering indicator of the Anthropocenethem as recent [4]. and precise indicators of earth deposits. Some authors identify the period from 1945 onwards as a moment of a significant increase in Plasticplastics materials deposition, can to be the used point as that stratigraphic they have used markers this stratigraphic in the marker archaeological as an excellent field indicator by considering them as recent[13]. and precise indicators of earth deposits. Some authorsFigure 1 identify shows a famous the period picture taken from by 1945 Spanish onwards students during as a momenta university of trip. a In significant the photo, increase in plasticsthe deposition, flood level river to thein the point canyon that bed they is well-recorded have used thanks this to stratigraphic the deposition markerof plastic micro- as an excellent fragments that by now have been well-mixed with the sedimentary curly making up the canyon. indicator [13].We found a similar situation in Southern Italy; indeed, in Figures 2 and 3, it is possible to observe Figurethat1 showsplastics awere famous even used picture to fill taken the road by surf Spanishace, probably students to obtain during a double a university advantage: trip.no In the photo, thedisposal flood costs level for river materials in the and canyonno costs for bed the isuse well-recorded of suitable materials thanks (excavated to the rocks). deposition of plastic micro-fragmentsAccording that by to now the layers, have beenonce well-mixedaccumulated and with stratified, the sedimentary the sediment curly, which making consists up of the canyon. fragments of various plastic sizes, can have a good conservation potential that is comparable to that We foundone of a recalcitrant similar situation organic infossils. Southern Such synthetic Italy; indeed, fossil-based in Figures materials2 and are3 ,so it isabundant possible and to observe that plasticswidespread were even on usedEarth that to fill we the can roadconsider surface, them “tec probablyhnofossils” to obtainas they awill double constitute advantage: a perennial no disposal costs for materialsproof of the and existence no costs of humans for the on useEarth of [4] suitable to the point materials of being able (excavated to define this rocks). historical epoch as the Plasticene [14,15]. Figure 1. Appearance of the deposition and stratification of plastic materials in a Spanish canyon Figure 1. Appearance of the deposition and stratification of plastic materials in a Spanish canyon (Source: [16]). (Source: [16]). Int. J. Environ. Res. Public Health 2020, 17, 1212 3 of 27 Figure 2. Layering of plastic materials in an area of Southern Italy. Figure 2. Layering of plastic materials in an area of Southern Italy. Figure 3. Detail of the plastic stratigraphy. 2. Plastics and Co-Contaminants Microplastics (MPs) are defined by [17] as “synthetic solid particles or polymeric matrices, with regular or irregular shape and with size ranging from 1 μm to 5 mm, of either primary or secondary manufacturing origin, which are insoluble in water.” A key concern of microplastics pollution is whether they represent a risk to ecosystems and human health. However, there is much uncertainty associated with this issue. Data on the exposure and effect levels of microplastics are therefore required to evaluate the risk of microplastics to environments and human health. The adverse effects on organisms that are exposed to microplastics Int. J. Environ. Res. Public Health 2020, 17, 1212 3 of 27 Int. J. Environ. Res. Public Health 2020, 17, 1212 3 of 26 Figure 2. Layering of plastic materials in an area of Southern Italy. Figure 3. Detail of the plastic stratigraphy. Figure 3. Detail of the plastic stratigraphy. 2. PlasticsAccording and Co-Contaminants to the layers, once accumulated and stratified, the sediment, which consists of fragments of variousMicroplastics plastic sizes,(MPs) canare defined have a goodby [17] conservation as “synthetic potential solid particles that is or comparable polymeric matrices, to that one with of regularrecalcitrant or irregular organic fossils.shape and Such with synthetic size ranging fossil-based from 1 materials μm to 5 mm, are so of abundant either primary and widespread or secondary on manufacturingEarth that we can origin, consider which them are “technofossils” insoluble in water.” as they will constitute a perennial proof of the existence of humansA key onconcern Earth [of4] tomicroplastics the point of beingpollution able is to whether define this they historical represent epoch a risk as the to Plasticeneecosystems [14 and,15]. human health. However, there is much uncertainty associated with this issue. Data on the exposure 2. Plastics and Co-Contaminants and effect levels of microplastics are therefore required to evaluate the risk of microplastics to environmentsMicroplastics and human (MPs) are health. defined The by adverse [17] as effects “synthetic on organisms solid particles that are or polymericexposed to matrices,microplastics with regular or irregular shape and with size ranging from 1 µm to 5 mm, of either primary or secondary manufacturing origin, which are insoluble in water.”. A key concern of microplastics pollution is whether they represent a risk to ecosystems and human health. However, there is much uncertainty associated with this issue. Data on the exposure and effect levels of microplastics are therefore required to evaluate the risk of microplastics to environments and human health. The adverse effects on organisms that are exposed to microplastics can be separated into two categories: physical effects and chemical effects. The former is related to the particle size, shape, and concentration of microplastics, and the latter is related to hazardous chemicals that are associated with microplastics.