Comparing The Impacts Of Sediment-Spiked Cadmium On Chironomidae Larvae In Laboratory Bioassays And Field Microcosms And The Implications For Field Validation Of Site-Specific Threshold Concentrations

Information on the effects of pollutants in sediments at an ecosystem level to validate current and proposed risk-assessment procedures is scarce. The most frequent criticism of these procedures is that responses of surrogate species in the laboratory are not representative of responses of natural populations. A tiered approach using both laboratory and microcosm exposures (96-h and 21-d laboratory bioassays and a 3-mo field microcosm) was conducted to compare the impacts of sediment-spiked cadmium on the mortality, development, and abundance of Chironomidae larvae. The 96-h and 21-d lethal concentrations of sediment-spiked Cd to 50% of the species Chironomus riparius were estimated to be 201.07 and 172.66 mg/kg, respectively. In the 21-d laboratory bioassay, the endpoints, including the development rate and emergence ratio, were compared, and the lowest-observed-effect concentration (LOEC) values were 325.8 and 10.7 mg/kg, respectively. The abundance, richness, and biomass of field-collected larvae were compared among the different treatments in the field microcosm, and it was found that the order of sensitivities using different endpoints was biomass (2.6/5.2 mg/kg of no-observed-effect concentration/LOEC) > diversity (10.7/21.2 mg/kg) > abundance (41.2/82.7 mg/kg). The toxicity values based on lethal/sublethal changes in the laboratory bioassays might not fully protect field organisms against damage from chemicals, such as Cd, unless an assessment factor of 5 is used. These findings highlight the need to conduct field validation of criteria/guidelines before they are introduced to protect organisms/ecosystems in the field and provide a preliminary template for future field validation of criteria elsewhere. Environ Toxicol Chem 2021;00:1-13. (c) 2021 SETAC