Bioavailability of Polychlorinated Dibenzo-p-dioxins in Lake Enclosures

The bioavailability of 1,3,6,8-tetra- (T4CDD) and octachlorodibenzo-p-dioxin (O8CDD) was examined in large (40 m3) lake enclosures at the Experimental Lakes Area in northwestern Ontario. The polychlorinated dioxins (PCDDs) were added to replicate enclosures as a sediment slurry at a nominal concentration of 58–59 ng∙L−1. T4CDD was more bioavailable to caged benthic invertebrates and fish (white sucker, Catostomus commersoni) than O8CDD immediately after the addition to the enclosures. However, as the concentration of T4CDD in the water column rapidly declined, the bioavailability of T4CDD also declined. Sorption of PCDD to organic matter and rapid partitioning to sediments might have reduced the uptake of PCDDs directly from the water column. Accumulation of PCDDs in biota appeared to shift from direct equilibrium partitioning during the first few days, when the concentrations in the water column were relatively high, to a detrital food chain transfer as the freely available PCDDs in the water declined. This conclusion is supported by the results of the simple, four-compartment food chain model of Thomann and Connolly based on the uptake kinetics of PCDDs from water and food.

Bacterial succession during biodegradation of the kelp Alaria esculenta (L.) Greville

In northern latitudes large quantities of kelp can be dislodged by ice scouring during spring and early summer. Quantities of kelp are then available to enter the detrital food chain. Bacterial succession, on decaying fronds of the brown macroalga Alaria esculenta, was investigated. There was a loss of approximately 70% of the algal mass during late spring and summer. During this time Vibrio dominated the heterotrophic bacterial population. Species of marine Pseudomonas comprised about 10–30% of the population, depending upon the occasion of isolation. By using numerical taxonomy it was shown that the strains of Vibrio formed distinct and separate clusters according to the occasion on which they were isolated. Among Pseudomonas strains a more gradual change was observed, but by the time of the final isolation, the Pseudomonas strains were different from those isolated at the beginning of the study. The results of characterization tests showed that strains from all clusters were suited to growth on substrates which are components of brown algae and that a succession of bacterial species, of more than one genus and family, occurred during the decay process.