Soil invertebrate avoidance behavior identifies petroleum hydrocarbon contaminated soils toxic to sensitive plant species

In recent years, laboratory soil toxicity testing has advanced with the introduction of ecologically relevant boreal forest soil invertebrate and plant species, as well as increased adoption of avoidance toxicity tests. In this study, we investigated the toxicity of a binary petroleum hydrocarbon (PHC) mixture to six agronomic and boreal forest plant species (Elymus lanceolatus, Lactuca sativa, Medicago sativa, Raphanus sativus, Pinus banksiana and Picea glauca) and the avoidance response of five soil invertebrate species (Eisenia fetida, Enchytraeus crypticus, Folsomia candida, Oppia nitens and Hypoaspis aculeifer). We assessed concentration addition and independent action mixture toxicity reference models, with potential interactions, using observed responses from the mixture and individual component toxicity endpoints from literature. Our key finding was soil invertebrate avoidance of PHC-contaminated soil was in the similar range of growth measurements for plant species sensitive to PHC-contaminated soils. This study further supports the inclusion of avoidance tests in toxicity test batteries for assessing PHC toxicity as invertebrate avoidance response appears to be linked to plant growth and informative of plant habitat quality.