Ecotoxicity test methods for engineered nanomaterials: Practical experiences and recommendations from the bench

Abstract

Ecotoxicology research is using many methods for engineered nanomaterials (ENMs), but the collective experience from researchers has not been documented. This paper reports the practical issues for working with ENMs and suggests nano-specific modifications to protocols. The review considers generic practical issues, as well as specific issues for aquatic tests, marine grazers, soil organisms, and bioaccumulation studies. Current procedures for cleaning glassware are adequate, but electrodes are problematic. The maintenance of exposure concentration is challenging, but can be achieved with some ENMs. The need to characterize the media during experiments is identified, but rapid analytical methods are not available to do this. The use of sonication and natural/synthetic dispersants are discussed. Nano-specific biological endpoints may be developed for a tiered monitoring scheme to diagnose ENM exposure or effect. A case study of the algal growth test highlights many small deviations in current regulatory test protocols that are allowed (shaking, lighting, mixing methods), but these should be standardized for ENMs. Invertebrate (Daphnia) tests should account for mechanical toxicity of ENMs. Fish tests should consider semistatic exposure to minimize wastewater and animal husbandry. The inclusion of a benthic test is recommended for the base set of ecotoxicity tests with ENMs. The sensitivity of soil tests needs to be increased for ENMs and shortened for logistics reasons; improvements include using Caenorhabditis elegans, aquatic media, and metabolism endpoints in the plant growth tests. The existing bioaccumulation tests are conceptually flawed and require considerable modification, or a new test, to work for ENMs. Overall, most methodologies need some amendments, and recommendations are made to assist researchers.