No abstract

The behavioural response and survival of marine mud snails and mud shrimp exposed to freshwater and the fungicide chlorothalonil (tetrachloroisophthalonitrile) was investigated. Amphipods were less tolerant of lower salinity than snails, with 50 and 76% survival associated with 5 and 0% seawater in freshwater, respectively. However, 50% of snails displayed a defence mechanism by retracting within their shell when exposed to 70% freshwater. Both species displayed an avoidance to chlorothalonil spiked at >100 ng/g and/or >100 ng/mL in sediments and seawater, respectively. The avoidance response of amphipods was observed along with a reduced swimming ability and increased lipid content. Snails displayed a higher susceptibility to physical stress, with an increased number unable to twist from being on their shell to their foot, and with longer righting time. Behaviour was affected at chlorothalonil concentrations of 0.001-0.01 ng/g and/or ng/mL, with a variability that could be due to degradation by the microbial community. Ascertaining the latter observations requires state-of-the-art chemical analyses.

Pesticides sprayed on farmlands can end up in rivers and be transported into estuaries, where they could affect aquatic organisms in freshwater and marine habitats. A series of experiments were conducted using the amphipod Corophium volutator Pallas (Amphipoda, Corophiidae) and single pesticides, namely atrazine (AT), azinphos-methyl (AZ), carbofuran (CA) and endosulfan (EN) that were added to sediments and covered with seawater. Our goal was to compare the concentrations affecting the survival of the animals relative to potential attractant or repellent properties of sediment-spiked pesticides. The avoidance/preference of contaminated/reference sediments by amphipods was examined after 48 and 96 h of exposure using sediments with different organic carbon content. The octanol-water partition coefficients (log K(ow)) ranked the pesticides binding to sediments as EN > AZ > AT > CA. LC(50) and LC(20) covered a wide range of nominal concentrations and ranked toxicity as CA-AZ > EN > AT. Under the experimental set up, only EN initiated an avoidance response and the organic carbon normalised concentration provided consistent results. Using the present data with wide confidence limits, >20% of a population of C. volutator could perish due to the presence of EN before relocation or detecting CA or AZ in sediments by chemical analysis.

Applications of pesticides in areas of agricultural production have been an environmental concern for the past several decades. Varying-sized watersheds draining regions of intense agriculture in the Maritime Provinces of Canada were monitored between 2003 and 2007 to determine the major in-use pesticides and to gain an understanding of the risks posed to aquatic ecosystems. A questionnaire collected from farmers in one watershed intensively cropped with potato indicated that 43 pesticides were applied with 18 of them being detected in that watershed. Our results across the Maritime region suggested that detection frequencies ranged from 0.0 to 22 % during the study period. Chlorothalonil, linuron, metalaxyl, and metribuzin were detected in 17-22 % of samples collected during rainfall events every year. Other pesticides, such as azinphos-methyl, atrazine, cypermethrin, permethrin, fonofos, and β-endosulfan were detected in ≤17 % of the samples during some years of the study. Concentrations of several pesticides were found to exceed their Canadian Council of Ministers of the Environment (CCME) aquatic life water-quality guidelines in pulses after rain events. The highest proportion of detections exceeding a CCME guideline was for chlorothalonil at 12.9 %, β-endosulfan at 6.0 %, and linuron at 3.4 %. Despite indications that remedial measures offer protection to aquatic environments, spatial and temporal gaps in the data prevented a full evaluation. A dedicated long-term multiple-watershed monitoring program for this region of Canada is therefore recommended.