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Latebreaking Poster

Session: Environmental Impact And Risk Assessment (Latebreaking)

LB 19-174 - Avoidance behavior to toxicity testing of Oppia nitens in heavy metal and microplastic spiked soils.

Thursday, August 10, 2023
5:00 PM – 6:30 PM PDT
Location: ESA Exhibit Hall
Environment and Climate Change Canada recently completed a standardized protocol of ecotoxicity testing for Oppia nitens, a soil oribatid mite that performs crucial functions to support ecosystem services. Consequently, O. nitens is now recommended among the class of soil invertebrates for toxicity testing, however, its applicability is limited by the paucity of data on its avoidance behavior to contaminants in soils. In this study, we examined the avoidance behavior of O. nitens to three concentrations of copper (1280, 2500 and 5000 mg/kg soil) and two concentrations of microplastic - polyvinyl chloride/PVC (2500 and 5000 mg/kg soil) following standardized guidelines. The O. nitens were exposed to the concentrations for 48 hours using a two-chamber test. With the two-chamber method, the oribatid mites had the choice between clean artificial and contaminated soils. Our results showed that O. nitens avoided the contaminated copper soils at higher concentrations (2500 and 5000 mg/kg) and the higher concentration of contaminated PVC soil (5000 mg/kg) as shown by the positive net response of the mites. However, the mites had an attraction to the lower concentrations of the contaminated copper (1280 mg/kg) and PVC (2500 mg/kg) soils which was shown by the negative net response. Attraction to low levels of contaminants has been termed hormesis especially if they are minutely required for normal metabolism, such as in copper. However, the hormesis-like pattern observed for PVC in this study could not be explained since microplastic is not a requirement for metabolic activities in mites compared to such attractions in low concentrations of copper and zinc as reported in other studies. The O. nitens is a promising species for avoidance testing in soil ecotoxicology and of great ecological relevance for assessing soils contaminated with metals, organic pollutants and microplastics. Since this is the first study investigating O. nitens avoidance to microplastic spiked soils, more experiments are needed to evaluate its net responses to varying chemical classes and concentrations in laboratory tests and applicability in contaminated ecosystems.