Environmental risk assessment of crude oil in Lemna minor, Daphnia magna, and Danio rerio

Oils spills cause aquatic pollution generating serious environmental problems. In the present study, we assessed the aquatic environmental risk of crude oil by determining lethal and sublethal effects in Lemna minor, Daphnia magna, and Danio rerio. We determined the toxicity of total petroleum hydrocarbons (TPH) establishing the water-accumulated fractions of petroleum. Bioassays were evaluated using a 6 x 4 randomized complete block design (RCBD) with five concentrations plus control and four repetitions. We evaluated the dry weight and chlorosis in L. minor, the mortality and immobility in D. magna, and the hypoactivity, bottom scape, and hypoventilation in D. rerio. In the results, we considered the differences (p<0.05) between concentrations and the control. The concentration at which no effect from exposure to the contaminant was observed (NOEC) was <0.4 and 3.22 mg/L for chlorosis and dry weight in L. minor. In the case of water fleas, we obtained a median effective concentration for immobility (EC_50-48h) of 2.74 mg/L and a median lethal concentration for mortality (LC_50-48h) of 6.22 mg/L. For fish bioassays, the NOEC and the lowest concentration at which an effect was observed (LOEC) of the hypoactivity parameter were 14.28 and 28.61 mg/L, respectively. The bottom scape effect occurred in 100% of the fish at 3.58 mg/L. As for hypoventilation, the NOEC and LOEC were 7.15 and 14.31 mg/L measured at 96 h. The decreasing ecotoxicity order was as follows: L. minor (<0.40 mg/L – chlorosis at 168 h) > D. magna (1.61 mg/L – immobility at 48 h) > D. rerio (<3.58 mg/L – bottom scape at 96 h). The risk quotient was higher than 1, which evidenced the environmental aquatic risk.