ORGANIC CONTAMINANTS IN SUBMERSED MACROPHYTES DRIFTING IN THE DETROITRIVER

Macrophytes drifting in the Detroit River were sampled and analysed fo r contaminants at monthly intervals from September 1990 to September 1 991. Twelve species of submersed macrophytes were identified, as well as algae and leaves of terrestrial plants. Drifting plant debris was g reatest in August-September, when Potamogeton spp. and Najas sp. predo minated. Over the study period, a total of 60.57 x 10(6) kg fresh mass (3.0285 x 10(6) kg ash-free dry mass) of plant debris drifted out of Lake St. Clair into the Detroit River annually. Organochlorine content differed between plant taxa and according to the time of year. Annual contaminant burden of the Detroit River by upriver contributions was carried mostly by Potamogeton spp. and Najas sp. Total annual load of organochlorines in drifting plant debris was estimated to be 155 g, in cluding 124 g of PCBs. These bioavailable contaminants may enter the d etrital compartment of aquatic food webs, following plant senescence, or may be taken up directly by herbivores. Contaminants associated wit h plant debris drifting from Lake St. Clair and the Detroit River cont ribute a significant burden of bioavailable organic contaminants to th e western basin of Lake Erie.