Response of river otters to experimental exposure of weathered crude oil: Fecal porphyrin profiles

Profiles of porphyrins were characterized in fecal samples from river otter s (Lontra canadensis) experimentally exposed to weathered crude oil to dete rmine effects on heme synthesis. Fifteen male river otters were randomly as signed to th ree groups of five individuals each representing a control gro up, a low-dosage group that received 5 mg/ kg body mass of oil per day, and ;a high-dosage group that received 50 mg/kg body mass of oil per day. Mean levers of coproporphyrin III (CoproIII) and protoporphyrin IX (ProtoIX) in fecal samples collected from all experimental river otters were higher thro ughout the experimental period than levels of CoproIII and ProtoIX in fecal samples collected previously at two field sites. No statistically signific ant differences in levels of CoproIII and ProtoIX were observed between tre atment groups, although a trend of reduction in variability in CoproIII was observed in the low- and high-dose groups. We found no relation. between l evels of CoproIII and ProtoIX, suggesting that the process of disruption th at leads to oxidation of the precursors of porphyrins is probably nonlinear . Our results also indicate that the interaction between oiled induced redu ction in hemoglobin levels and induction of CYP1A1 corresponded with signif icantly lower levels of ProtoIX in the fecal samples, possibly representing high demand for ProtoIX. Therefore, while this experiment does not support the use of porphyrin profiles as an individual biomarker, it does suggest that the latter may be valuable when a weight of evidence is used in an eco toxicological risk assessment in which the interactions between several bio markers are explored.