Organisms can adapt to increasing ROS production

Organisms can adapt to increasing ROS production by up-regulating antioxidant defences, such as the activities of antioxidant enzymes (Livingstone, 2003). Failure of antioxidant defences to detoxify excess ROS production can lead to significant oxidative damage including enzyme inactivation, protein degradation, DNA damage and lipid peroxidation (Halliwell and Gutteridge, 1999). In particular, lipid peroxidation is considered to be a major mechanism by which oxyradicals can cause tissue damage, leading to impaired cellular function and alterations in physicochemical properties of cell membranes, which in turn disrupt vital functions (Rikans and Hornbrook, 1997). This study focuses on the Llobregat river basin (NE Spain), which supplies water to many urban areas including the city of Barcelona and is a good example of an intensively used Mediterranean stream system, receiving extensive urban, agricultural and industrial waste water discharges and with low to moderate natural flows (0.1–12m3/s). In previous studies the presence of endocrine disrupters and of persistent organic pollutants in those waters and their bioavailability and effects on carps (Cyprinus carpio) and crayfish (Procambarus clarkii) in terms of alteration of normal levels of vitelogenin, cytochrome P450 and phase II enzymes were shown (Solé et al., 2000, Fernandes et al., 2002). However, there are no data available on the bioavailability of other chemicals, such as metals, nor their toxicological effects on macroinvertebrate benthic species, despite the fact that they are used to measure the ecological status of river ecosystems (Clarke et al., 2003). The present study was conducted to integrate chemical analyses of selected metals in animal tissue with antioxidant enzyme and lipid peroxidation responses, and measures of ecological quality using physicochemical water parameters and measurements of SYR-322 structure focused on benthic macroinvertebrates. This makes it possible to investigate whether resident organisms within the benthic macroinvertebrate community are responsive to changes in water quality and therefore suitable for biomonitoring environmental pressures due to contaminants. Caddisfly larvae of the pollution-tolerant macroinvertebrate species Hydropsyche exocellata (Trichoptera) were selected as sentinel organisms due to their wide distribution, relatively large size (20–100mg wet weight), and abundance along polluted areas within the studied river systems (Bonada et al., 2004). H. exocellata has a variable life cycle with two to several generations per year (Bonada, 2003) and therefore specimens from the last instar can be found throughout the year. Caddisfly larvae have been regarded as an appropriate group to assess water quality (Resh, 1992), and to biomonitor metal contamination due to their ability to bioaccumulate metals (Cain and Luoma, 1998, Cain et al., 2004, David, 2003, Evans et al., 2002). Furthermore, caddisfly larvae feed collecting algae and detritus and have a key role transferring energy from producers to invertebrate and vertebrate predators (Resh, 1992). Thus, the measured contaminant levels and toxicological effects in these organisms are likely to propagate through out the river food web in terms of contaminant and food transfer to higher trophic levels, respectively (Baird and Burton, 2001).
Materials and methods
Results
Discussion Physicochemical water parameters and metal concentration levels determined in caddisfly larvae indicated a clear increase of organic and metal pollution from upper to downstream reaches in the Llobregat river system, with contaminant metal loading increasing in summer when water flow diminished. These results are characteristic of Mediterranean regions, where intensive water resource use is frequently linked to the lack of water flow due to climatic constrains, and rivers can receive effluents from cities, industries and agriculture with little dilution in summer. In this situation water quality is poor, and measures that are effective for wet countries, such as the building of wastewater treatment plants fail to recover river water biological quality (Prat and Munné, 2000).