Assessment of River Po Sediment Quality by Micropollutant Analysis Marina Camussoa,*, Silvana Galassib, Davide Vignatia
Total Page：16
File Type：pdf, Size：1020Kb
Water Research 36 (2002) 2491–2504 Assessment of river Po sediment quality by micropollutant analysis Marina Camussoa,*, Silvana Galassib, Davide Vignatia a Water Research Institute, C.N.R., Via della Mornera 25, 20047 Brugherio, Milan, Italy b University of Insubria, Via Valleggio 11, 22100 Como, Italy Received 2 January 2001; accepted 19 October 2001 Abstract Trace metals, PCB congeners and DDT homologues were determined in composite sediment samples collected from 10 representative sites along the river Po in two separate seasons. The aim was to identify the most anthropogenically impacted areas for future monitoring programmes and to aid development of Italian sediment quality criteria. The surface samples were collected during low flow conditions. Trace metal concentrations were assayed by electrothermal (Cd, Co, Cr, Cu, Ni, Pb), flame (Fe, Mn, Zn) or hydride generation (As) atomic absorption spectrometry after microwave assisted acid digestion. Hg was determined on solid samples by automated analyser. Organic microcontaminants were determined by gas-chromatography with 63Ni electron capture detector after Soxhlet extraction. Concentrations of trace metals, total PCB and DDT homologues showed two distinct peaks at the sites immediately downstream of Turin and Milan, respectively, and in each case decreased progressively further downstream. Principal component analysis identified three major factors (from a multi-dimensional space of 35 variables) which explained 85–90% of the total observed variance. The first and second factors corresponded to anthropogenic inputs and geological factors on sediment quality; the third included seasonal processes of minor importance. Sediment quality assessment identified Cd, Cu, Hg, Pb, Zn and organic microcontaminants as posing the most serious threats to river sediment quality. A reference site within the Po basin provided useful background values. Moderate pollution by organochlorine compounds was ascribed both to local sources and to atmospheric deposition. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Organochlorine compounds; Trace metals; Sediment quality; River Po 1. Introduction lakes. However, in view of the persistence of many micropollutants and their potential for bioaccumula- Sediments are a recognised sink and reservoir for a tion, sediments are now regarded as an important source variety of environmentalcontaminants, includingboth of many micropollutants that seriously threaten natural naturally occurring substances subject to anthropogenic ecosystems [1]. Developing reliable methods for estimat- influences (e.g. nutrients and trace metals) and xenobio- ing the risks due to these substances in aquatic tic compounds (PCB, PAH, etc.). In the past attention environments has therefore become a priority. To concentrated on the role of sediments as a reserve complicate matters, many new chemicals have been compartment in the biogeochemicalcycleof phos- introduced into the biosphere so recently that their phorus, and as a source of phosphorus in eutrophic potential bioavailability and toxic effects are still unknown. Risk assessment must therefore be based on *Corresponding author. Tel.: +39-039-2004303; fax: +39- a few classes of inorganic and organic chemicals that 039-2004692. have been widely studied in both abiotic and biotic E-mail address: [email protected] (M. Camusso). matrices. 0043-1354/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII: S 0043-1354(01)00485-7 2492 M. Camusso et al. / Water Research 36 (2002) 2491–2504 Trace metals and organochlorine compounds are (September-October) 1996 and winter (February- among the most frequently monitored micropollutants, March) 1997. Samples from each site at each date were and reliable techniques have been established for their pooled to provide composite samples for analysis. extraction and quantification. The data available on Medium flow conditions prevailed on both sampling sediments have made it possible to propose sediment occasions, but discharge, measured at the Pontelagos- quality criteria and guidelines for these contaminants, curo (PLS) monitoring station, was more stable in which in some cases have been endorsed by environ- winter and two major high flow events (maximum mental protection agencies [2,3]. However, the reliability discharges at PLS=5570 and 6870 m3 sÀ1) occurred of the numericalcriteria has not been establishedand between the two campaigns (Fig. 1). extensive field validation is necessary before these At each site samples were taken with a Ponar grab criteria can be routinely used for large-scale monitoring sampler along longitudinal transects of varying length [4]. Regrettably, natural background levels of trace (from 1–2 km in the upper stretches of the river to 20– metals and baseline pollution levels of xenobiotic 40 km in the lower reaches). The samples from each compounds are still unknown for many important transect were thoroughly mixed in situ under dim light freshwater ecosystems, and this often hinders the conditions and transported on ice to the laboratory [9]. establishment of reliable and widely applicable sediment After freeze-drying, whole sediment sub-samples were quality criteria. sieved through a standard sieve (ASTM no 230, Fritsch) All these problems apply to the river Po, the largest and the fraction less than 63 mm was employed for trace Italian river (and tenth largest European river in terms metal and organic micropollutant analysis [10]. Site 1 of length and basin area). Although studies on sediment (Monte Torino), only 75 km from the source and contamination in some stretches of the Po have been upstream of all major anthropogenic influences, served performed [5] and references therein [6–8]; systematic as reference site. All the other sites (2–10 in Fig. 1) were investigations have not been conducted along the entire downstream of the confluences of the Po’s main course. The present study, which is part of a compre- tributaries: Dora Riparia, Dora Baltea, Sesia, Tanaro, hensive research project being carried out by the Italian Ticino, Lambro, Adda, Oglio and Panaro. In what Water Research Institute (IRSA-CNR), is the first follows, each sampling site is referred to mainly by the attempt to fill this gap. numbers in Fig. 1 but also by the name of the tributary. Spatialand seasonalvariations of trace metals,PCB As shown in Fig. 1, the study focused on the Alpine congeners and DDT homologues were investigated tributaries (left bank of the Po) rather than Apennine almost simultaneously (all sites were visited within 2 (right bank) tributaries since the former normally have weeks) at 10 representative locations evenly distributed much higher discharges, and much greater contaminant along the course of the river. Composite sediment loads. However, two Apennine tributaries were included samples were taken from each site in order to identify in the study: the Tanaro (site 5) which is the main the most anthropogenically impacted areas and also tributary in the upper Po and the Panaro (site 10) which identify priority compounds for future monitoring. is the last tributary of the Po. Downstream of the Overall sediment quality was also evaluated with respect confluence with the Panaro, the Po becomes estuarine to recently calculated numerical criteria. We are fully and its bed is above the level of the surrounding terrain. aware of the limitations of this type of evaluation which Site 10 is therefore in the closing section of the river. was performed with a view to developing Italian sediment quality criteria (as proposed by Italian 2.2. Trace metal analysis Legislative Decree 152, 11 May 1999). The findings of this study constitute the first set of homogeneous data Aliquots of approximately 0.1 g of sediment material for the contaminants investigated in the river Po. While (o63 mm) were weighed into acid-cleaned TFM vessels investigation of the time trends of sediment contamina- and digested with 5 mlof a mixture of nitric, hydro- tion in the river was beyond the scope of the study, it chloric and hydrofluoric acid (3:1:0.5) in a 1000W provides two time-separated but fully comparable microwave oven (Milestone 1200 MDR 1000/6/100/110) snapshots of sediment quality in the Po for some of operated at 35–50% of maximum power for 20 min. This the most toxic and persistent micro-contaminants. procedure proved suitable for the material from sites 6– 10 (lower Po) but did not completely digest sediments from sites 1–5 (upper Po). For the latter samples, 2. Materials and methods complete dissolution was achieved by adding 3.5 ml of a saturated solution of boric acid in hydrofluoric acid to 2.1. Sampling the standard acid mixture (EPA method 3052–95). After dissolution, the vessels were cooled to room temperature Sediment samples were collected at 10 sites along the and the solutions transferred to pre-conditioned poly- main course of the river (Fig. 1) in late summer thene vials, made up to 50 ml with deionised (Milli-Q) M. Camusso et al. / Water Research 36 (2002) 2491–2504 2493 Fig. 1. Sampling stations along the river Po: 1=Monte Torino (MT), 2=Dora Riparia (DR), 3=Dora Baltea (DB), 4=Sesia (SE), 5=Tanaro (TA), 6=Ticino (TI), 7=Lambro (LA), 8=Adda (AD), 9=Oglio (OG), 10=Panaro (PA). Flow regime measured downstream station 10 over the period September 1996FMarch 1997 is shown in the box. water, and stored at 41C pending analysis. All digestions elements except Cd (15%). Closely similar RSDs (n ¼ 3) were performed in triplicate and procedural blanks were were found for the reference material, indicating that the routinely included to check for ambient or reagent adopted protocols were suitable for trace metals contamination. Trace metals were determined by elec- determination in the river Po sediments. trothermalatomic absorption spectrometry with deuter- ium background correction (Cd, Co, Cr, Cu, Ni and 2.3. Organic pollutant analysis Pb), air/acetylene flame absorption spectrometry (Fe, Mn and Zn), or hydride generation (As). Hg was Aliquots of 2 g of lyophilised sediment (o63 mm) were determined directly on solid samples on an automated extracted for 8 h in a Soxhlet with pesticide-grade n- Hg analyser (AMA254, FKV, Bergamo, Italy).