Sediment reworking rates of Stylodrilus heringianus (Oligochaeta: Lumbriculidae) were measured in microcosms containing sediments dosed with the chlorinated pesticide, endrin. Reworking rates were measured at 10°C by monitoring a ~37cesium marker layer burial in contaminated and uncontaminated microcosms. Endrin concentrations ranged from 3.1 to 42 000 ng/g dry sediment. Alterations in reworking rates were observed at sediment concentrations five and one half orders of magnitude below the LCs0 (1 650 #g/g). For the lower concentrations, marker layer burial rate data suggested possible stimulatory effects in the first 300 to 600 h, followed by significant rate decreases relative to controls. For higher concentrations, rates were equal to or slower than control rates in the first 600 h, followed by dramatic decreases in the last 600 h. High final surficial sediment endrin concentrations at the end of experiments implied worm mediated upward transport. Worm mortalities were 9.3 to 28% for the two highest concentrations (42 000 and 11 500 ng/g) and 0 to 6.7% for all other concentrations including controls. Post experimental worm dry weights were inversely related to high concentrations. Bioaccumulation factors ranged from 34 to 67 on a g dry organism to g dry sediment basis.
Mean 96-hr LCs0 values and standard deviations for the oligochaetes S. heringianus and L. hoffmeisteri exposed to endrin-contaminated sediment were 2,588 _ 1,974 txg/g dry weight sediment for 4 assays and 2,725 + 955 Cg/g for 2 assays, respectively. Mixed species testing data suggested that the toxicity to L. hoffrneisteri was reduced in the presence of S. heringianus, yet further testing is required. Ninety-six hour ECs0 burrowing avoidance values for both species (19 and 15.3 txg/g for S. heringianus and 59 ~xg/g for L. hoffmeisteri) were approximately 46 and 150 times lower than their respective mean 96-hr LCs0 values. Both S. heringianus and L. hoffmeisteri initially burrowed in
Sediment reworking by Limnodrilus hoffmeisteri (Tubificidae) alone, and with Stylodrilus heringianus (Lumbriculidae) were measured in sediments dosed with endrin by monitoring the burial of a 137cesium marker layer. Endrin concentrations ranged from 16.1 to 81 400 ng/g dry sediment weight. Alterations in reworking rates were observed at sediment concentrations two to five orders Of magnitude below LCso values. In single species experiments with L. hoffmeisteri at low endrin concentrations, marker layer burial rate data did not suggest stimulation of reworking, as had previously been found for S. heringianus. At higher concentrations, reworking rates were equal to or slower than control rates early in experiments, followed by dramatic decreases thereafter. Reworking rates with mixed species (1:1 species ratio) suggested that the presence of S. heringianus enhanced the reworking response of L. hoffmeisteri. Post-experimental worm dry weights were inversely related to high sediment concentrations for both species. Reductions in post-experimental L. hoffmeisteri mortalities and increases in L. hoffmeisteri dry weights in mixed species tests at high endrin concentrations implied that L. hoffmeisteri benefits from the presence of S. heringianus, although the reverse was not observed. High final sediment endrin concentrations in the upper three cm implied worm mediated upward contaminant transport. Bioaccumulation factors for S. heringianus ranged from 9.7 to 43.8 and were consistently three to four times greater than bioaccumulation factors for L. hoffmeisteri (1.7 to 13.6).
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