The effect of malathion 60 on Gammarus pulex (L.) below watercress beds

Uncertainty is always associated with extrapolations of laboratory toxicity test responsesto in situ conditions. Exposing toxicity test organisms in situ reduces uncertainty by removing sampling related artifacts and better simulating natural exposures. The amphipod Hyalella azteca and the midge Chironomus tentans, were enclosed in plastic containers with 149‐ or 74‐mm mesh openings. These chambers were anchored to stream substrates allowing continual water exchange and contact with sediments. Hyallela azteca survival was greater than 80% after 4 weeks of exposure. In situ testing with H. azteca in cold water (<15°C) resulted in survival consistently below 60%, possibly due to limited acclimation periods. Handling stress during laboratory to field transport reduced C. tentans survival. High survival was not consistently achieved until a protective ground paper towel substrate was used. A smaller mesh size (74 mm) on the chambers reduced the occurrence of indigenous organisms inside the chambers, making C. tentans identification unmistakable. In situ testing with C. tentans using refined methods resulted in greater than 80% survival after 2 weeks of exposure. In situ exposures of these two benthic invertebrates can effectively evaluate short‐ to long‐term conditions of water and sediment quality.

Section: Introductionmentioning

confidence: 99%

Optimization of in situ bioassays with Hyalella azteca and Chironomus tentans

Chappie

Burton

1997

Cholinesterase and glutathione‐S‐transferase activities in freshwater invertebrates as biomarkers to assess pesticide contamination

Domingues

Agra

Monaghan

et al. 2009

130

Abstract-Studies investigating the use of biomarkers in pesticide risk assessment have greatly increased in recent years; however, issues concerning the ecological meaning of enzymatic responses have proved controversial. Ideally a good biomarker response should be modulated by the environmental contaminants alone and demonstrate a predictable behavior towards certain types of toxins. As these premises are rarely observed, the present study aims to outline research that has contributed to an understanding of the behavior of two widely used biomarkers, cholinesterase and glutathione-S-transferase, describing environmental and biotic factors that affect their response in freshwater invertebrates. Studies were performed in the main classes of aquatic invertebrates with these biomarkers and conclusions were reached concerning their behavior towards the main classes of pesticides. Links between biomarker responses and conventional endpoints were evaluated so that ecological relevance could be attributed to enzymatic responses. Toxicity of mixtures was investigated, and cases of synergism and antagonism were pointed out as factors changing the expected toxicity of aquatic systems and leading to misinterpretations of biomarker responses. Finally, the use of biomarkers as a tool for biomonitoring and in situ assays was investigated, with discussion of advantages and disadvantages of their use.

Examining impacts of current‐use pesticides in Southern Ontario using in situ exposures of the amphipod Hyalella azteca

Bartlett

Struger

Grapentine

et al. 2016

In situ exposures with Hyalella azteca were used to assess impacts of current-use pesticides in Southern Ontario, Canada. Exposures were conducted over 2 growing seasons within areas of high pesticide use: 1 site on Prudhomme Creek and 3 sites on Twenty Mile Creek. Three sites on Spencer Creek, an area of low pesticide use, were added in the second season. Surface water samples were collected every 2 wk to 3 wk and analyzed for a suite of pesticides. Hyalella were exposed in situ for 1 wk every 4 wk to 6 wk, and survival and acetylcholinesterase (AChE) activity were measured. Pesticides in surface waters reflected seasonal use patterns: lower concentrations in spring and fall and higher concentrations during summer months. Organophosphate insecticides (chlorpyrifos, azinphos methyl, diazinon) and acid herbicides (2,4-dichlorophenoxyacetic acid [2,4-D], mecoprop) were routinely detected in Prudhomme Creek, whereas neutral herbicides (atrazine, metolachlor) dominated the pesticide signature of Twenty Mile Creek. Spencer Creek contained fewer pesticides, which were measured at lower concentrations. In situ effects also followed seasonal patterns: higher survival and AChE activity in spring and fall, and lower survival and AChE activity during summer months. The highest toxicity was observed at Prudhomme Creek and was primarily associated with organophosphates. The present study demonstrated that current-use pesticides in Southern Ontario were linked to in situ effects and identified sites of concern requiring further investigation.