Using radish (Raphanus lativus L.) germination to establish a benchmark dose for the toxicity of ozonated-petroleum byproducts in soil

The concentration-response relationship between the germination outcome of radish (Raphanus lativus L.) and ozonated petroleum residuals was determined experimentally. The outcomes were used to produce an ecological risk assessment model to predict the extra risk of adverse outcomes based on the concentration of ozonated residuals. A test soil with low organic matter (0.5% w/w) was mixed with raw crude oil, artificially weathered, and treated at three doses of ozone (O₃) gas (5 g, 10 g, and 40 g O₃ per 600 g of soil). Total petroleum hydrocarbons (TPH) and produced dissolved organic carbon (DOC) were measured. TREATMENT categories (control, petroleum, petroleum + 5 g O₃, petroleum + 10 g O₃, and petroleum + 40 g O₃) were then used to create a dilution series using different proportions of the test soil and a commercially available potting mix (∼75% w/w organic matter) to evaluate the effects of background organic matter (b-ORGANIC) in conjunction with TPH and DOC. Multivariable logistic regression was performed on the adverse germination outcome as a function of TPH, DOC, TREATMENT, and b-ORGANIC. The parameters controlling germination were the continuous variable DOC and the categorical variables TREATMENT and b-ORGANIC. Radish germination was strongly harmed by DOC from ozonation, but DOC's ecotoxicity decreased with increasing O₃ dose and the presence of b-ORGANIC beyond 10% (w/w). We used the germination outcome of radish to produce a logistic regression model that computes margins of DOC (± std. error) that create 10%, 25%, and 50% extra risk of adverse germination effects.