Degradation of weathered oil by mixed marine bacteria and the toxicity of accumulated water-soluble material to two marine crustacea

Artificially weathered crude oil was degraded by four diverse cultures of m ixed marine bacteria under optimized conditions for 7 and 14 days. Loss in total weight of starting oil (30 g) ranged from 6.8-17.3% in biologically a ctive incubations compared with only 0.9-1.1% in sterile and nutrient-limit ed controls. In all incubations, both neutral and acidic water-soluble frac tions (WSF) were accumulated. In biologically active systems, 50.9-249.0 mg neutral and 63.3-406.8 mg acidic WSF were accumulated whereas only 6.5-11. 1 mg neutral and 1.7-2.2 mg acidic WSF were accumulated in control incubati ons. Analysis by gas chromatography demonstrated that accumulated WSF in bi ologically active systems contained compounds different from those washed f rom the starting crude oil. Exposure of grass shrimp (Palaemonetes pugio) e mbryos to neutral WSF from each of the biologically active cultures resulte d in high embryo mortalities relative to sterile and nutrient-limited contr ols which exhibited >90% hatching success and larval survival. Toxicity of neutral WSF was also demonstrated on larvae of mysids (Mysidopsis bahia). I n both cases, toxicity occurred only on exposure to neutral material accumu lated by active, oil-degrading cultures and not with material washed from t he weathered crude oil. These results imply that unique compounds were accu mulated during degradation that may have been responsible for increased tox icity.