Pesticides and herbicides used in common agricultural practices, are applied only during specific periods of the year, leading to significant seasonal peak concentrations in fresh and coastal waters, particularly in spring after heavy rainfall (Pintar et al., 1996). The relatively high water solubility of some classes of herbicides (e.g. triazines), their low potential to adsorb onto soils and sediment (Meakins et al.,1995), their high leaching potential (Caracciolo et al., 2005) and persistence in the environment, can cause contamination of freshwaters, groundwater and coastal waters. Pesticides will partition among several compartments, i.e. water column –as dissolved and/or bound to dissolved and particulate organic carbon-, sediments – surface and deep sediments, interstitial waters-, aquatic organisms and atmosphere (Miyamoto et al., 1990). Herbicides are also subject to several chemical and physical transformations, which lead to its degradation in metabolites, which can be more or less toxic than the former molecules.
The persistence of these contaminants is extremely variable and depends on the above mentioned processes. Reported values vary from few hours to several years (e.g. Chung et al., 2003; Navarro et al., 2004, Kochany and Maguire, 1994). Impacts of herbicides in the aquatic ecosystem are both direct and indirect, spanning from instantaneous effects as massive mortality after an accidental contaminant release, to acute and/or chronic toxicity on sensitive species with alteration of the community structure, and long-term effects as bioaccumulation and biomagnification through the food web (Pérez-Ruzafa et al., 2000).
Ecotoxicological effects of pesticides on aquatic microorganisms (De Lorenzo et al., 2000) and plants (Forney, 1981) have been noticed; as well the toxic effects on humans are widely known (Funari, 1995). Furthermore, evidence exists that herbicides can produce additive and synergistic effects in algae (Strachan et al., 2001; Faust et al., 2001). Toxic effects have been also measured in mussels (Cheney et al., 1997) and clams (Lawton et al., 2005).
Recently, the European Commission introduced some herbicides in the list of “priority hazardous substances”, which are of particular concern for the European waters and which “will be subject to cessation or phasing out of discharges, emissions and losses within an appropriate timetable that shall not exceed 20 years” (Directive 2000/60/EC, Decision 2455/2001/EC). The priority and priority hazardous substances were chosen on the basis of toxicity, persistence and bioaccumulation criteria through the application of the environmental risk analysis. Monitoring activities and environmental risk assessment for these substances have been as well requested by the European Commission (93/67/EEC and Commission Regulation (No. 1488/94/EC). The Decision 2455/2001/EC ranks in order of priority the substances for which environmental quality standards and emission control measures will be set at Community level. In the last few years, several studies have shown presence of pesticides exceeding environmental quality standards proposed by national laws, in freshwaters, groundwater and coastal waters of many European States (e.g.: Konstantinou et al., 2005; Lekkas et al., 2004; Rodriguez-Mozaz, 2004; Cerejeira et al., 2003; Steen et al., 2002; Strandberg and Scott-Fordsmand, 2002; Lambropoulou et al. 2002). In particular, herbicide contamination has been noticed in Italian ground water and lakes (Galassi and Guzzella, 1990; Galassi, 1992; Della Vedova et al., 1996; Riparbelli et al., 1996), in fresh and coastal waters (Baldi et al., 1991; Coppi et al., 1999; Galassi et al., 1988; Giarei et al., 1996), sediment (Galassi et al., 2000; Baldi et al., 1991 ) and mussels (Baldi et al., 1994) of Emilia Romagna region, were a heavy load of herbicides comes from agricultural areas of Pianura Padana (the plain of the Po river).
Nevertheless, relatively few analytical field data are available for evaluating the environmental fate and impact of herbicides in aquatic ecosystems and there are very few studies on their metabolites and their environmental concentrations. Moreover temporal and spatial variations cannot be well described with few samples collected during sampling campaigns and measured concentration give poor information of real exposure.
For all these reasons, an integrated approach combining experimental data and ecosystem modelling is needed to determine exposure in aquatic ecosystems. A modelling approach will complement experimental data providing an estimation of the range of concentrations one should expect to find due to changes, for example, in water temperature, salinity, solar radiation, etc.
This is of particular concern for transitional water systems, as lagoons, estuaries, brackish ponds, which are physical and ecological boundaries between terrestrial and marine ecosystems. In particular coastal lagoons are shallow water bodies, connected to the sea through one or more canals, subject to sudden change in salinity (Kjerfve,
1994; Gönenç and Wolfin, 2005) with a high primary production sustained by loads of nutrients coming from agricultural inland areas and carried by rivers (Heip et al., 1995; Nedwell and Trimmer, 1996). In addition, coastal lagoons are subjected to strong anthropogenic pressures, as they receive freshwater inputs, rich in pollutants derived from urban, agricultural and/or industrial effluents and domestic sewage. Coastal lagoons present a wide range of different habitats, from the subtidal zone (permanently submerged) to the intertidal (which is affected by tides). Coastal
lagoons play a key role as spawning grounds for fish and shellfish and for this reason are also extensively exploited for aquaculture, especially for mollusc farming. Moreover, they are often important as bird’s reproduction and rest areas, and they present a rich and specific biodiversity, both for fauna and flora. Furthermore, port use and management, aquaculture and fishing are responsible for internal perturbations (pollution, sediment dredging, removal of indigenous species, changes in food web structure, etc.). Finally Mediterranean coastal lagoons are subjected to tourist pressures mainly during the summer season.