MA8 Toxicity of Complex Mixtures
Room 19A/B, Level 4
8:00 AM - 12:00 PM, Monday, 10 November 2003
Chair: Ren, Shijin ,
(079) Dynamics that Mediate the Joint Toxicity of Cd and PAH in a Freshwater Oligochaete.
Gust, K1, Fleeger, J1, 1 Dept. of Biological Sciences, Louisiana State University, Baton Rouge, LA, US
ABSTRACT- Bioassays were conducted employing Cd and phenanthrene as model toxicants to investigate the possible mechanisms involved in the joint toxicity of complex mixtures of metals and hydrocarbons. The bulk-deposit feeding sludgeworm Iylodrilus templetoni was exposed to sediment-amended Cd and phenanthrene eliciting antagonistic joint toxic responses for both lethality and tissue autotomy and independent responses for feeding rate and burrowing avoidance. A sublethal dose of phenanthrene in combination with Cd reduced the LC50 of Cd by 28.6% (95% C.I. 27.6-29.6%) and significantly reduced the frequency of tissue autotomy. The joint-toxicity of combined pollutants is influenced by contaminant chemistries, the relative bioavailability of each in the environment, uptake and depuration kinetics; and the toxicological modes of action, possible interactions, and detoxification mechanisms employed once accumulated by biota. Kinetic uptake of Cd from sediment into tissue was significantly enhanced by the presence of phenanthrene at all time-points (6, 12, 24 and 72h) and increased with increasing phenanthene concentration (3.2x at 72h for high phenanthrene doses). Enhancement of Cd uptake by phenanthrene did not appear to be the result of increased Cd bioavailability. Phenanthrene caused no significant increase in AVS concentration or dissolved Cd concentration in porewater and did not reduce pH. Elimination of cadmium from tissues was minimal and was not influenced by phenanthrene. Uptake kinetics and BSAF for phenanthrene were not significantly affected by Cd. Cadmium bioavailability and elimination rates were not affected by phenanthrene whereas phenanthrene actually increased the total body burden of Cd in worm tissues. The antagonistic joint toxicity of the combined pollutants cannot be explained by these results. Improved survivorship may be the result of enhanced metal detoxification such as metallothionein binding and incorporation of Cd into granules. Biomonitoring efforts often use body burden measurements and predictions of contaminant bioavailability to assess ecological health and assess toxicological risk to organisms in natural environments. As was demonstrated by our findings, this conventional wisdom may not be predictive for complex mixtures of metals and hydrocarbons.
Key words: PAH, metals, contaminant mixtures, sediment toxicity