Effects of boric acid on various microbes, plants, and soil invertebrates

Terrestrial ecotoxicology includes the investigation of the impact of chemicals on soils and soil-inhabiting organisms, whereby ecotoxicological effects are mainly assessed using single-species laboratory tests. As part of laboratory testing, reference substances, with known toxicity, are regularly used to confirm the sensitivity of the cultivated test organisms over time. Furthermore, reference substances are also applied in ring test evaluations for the validation of new test methods. The present work evaluates boric acid for its suitability as a potential reference substance for tests with higher plants and soil organisms (e.g., invertebrates and microbial communities). To enhance our existing knowledge, standardized acute and chronic laboratory tests with boric acid were performed and statistically evaluated using the following organism groups: microorganisms, higher plants, nematodes, enchytraeids, earthworms, collembolans, and beetles. The results demonstrated that boric acid was amenable for use in standardized laboratory tests using a wide range of microbes, plants, and soil invertebrates. Methodological problems were not identified. In addition, several organism groups demonstrated a hormetic response that must be taken into consideration when determining appropriate test concentration ranges for the use of boric acid as a reference substance. Finally, it was clear that the sensitivity of the different test species differed by about an order of magnitude (with the exclusion of microorganisms), which seems little when considering the wide taxonomic and physiological range of the organisms tested. Based on the present results boric acid can be considered as a suitable reference substance in soil ecotoxicology. It is also recommended that the suitability (i.e., sensitivity, robustness, and practicability) be proven in international ring tests.