Acetylcholinesterase inhibition in the threeridge mussel (Amblema plicata) by chlorpyrifos: implications for biomonitoring.

The effects of chlorpyrifos, an organophosphorus insecticide, were examined on the activity of the nervous system enzyme acetylcholinesterase (AChE) in the threeridge mussel Amblema plicata in a 24-day laboratory test. Thirty-six mussels in each of seven treatments (18 mussels per duplicate) were exposed to chlorpyrifos (0.1, 0.2, 0.3, 0.6, and 1.2 mg/L), a solvent (acetone), and a solvent-free (well water) control for 12, 24, or 96 h. The activity of AChE was measured in the anterior adductor muscle of eight mussels from each treatment after exposure. To assess potential latent effects, six mussels from each treatment were removed after 24 h of exposure and transferred to untreated water for a 21-day holding period; AChE activity was measured on three mussels from each treatment at 7 and 21 days of the holding period. The activity of AChE in chlorpyrifos-exposed mussels did not differ from controls after 12 or 24 h of exposure (t- test, P>0.05), but was significantly less than controls after 96 h (t- test, P=0.01). AChE activity did not vary among mussels at 24 h of exposure (i.e., Day 0 of holding period) and those at Day 7 and Day 21 of the holding period. Overall changes in AChE activity of mussels during the test were unrelated to individual chlorpyrifos concentrations and exposure times (repeated measure ANOVA; (P=0.06). A power analysis revealed that the sample size must be increased from 2 to 5 replicates (8 to 20 mussels per time interval and test concentration) to increase the probability of detecting significant differences in AChE activity. This calculated increase in sample size has potential implications for future biomonitoring studies with chlorpyrifos and unionid mussels.

Cadmium and mercury in emergent mayflies (Hexagenia bilineata) from the upper Mississippi River.

Burrowing mayflies (Hexagenia bilineata) were analyzed to assess longitudinal patterns in their cadmium and mercury content along the upper Mississippi River. Emergent mayflies (subimagoes and imagoes) were collected in 1988 at 34 sites (25 navigation pools), extending 1260 km from Little Falls, Minnesota, downstream to St. Louis, Missouri. Cadmium concentrations in composite samples of whole mayflies ranged from 7 to 219 ng/g dry weight in females and from less than 7 to 265 ng/g in males. Cadmium concentrations were highest (greater than or equal to 150 ng/g) in samples from Pools 2 and 3 (downstream from the Twin Cities metropolitan area), 15 (near the Quad Cities metropolitan area), and 27 (near the St. Louis metropolitan area). Cadmium concentrations in female mayflies decreased significantly with distance downstream from Pool 2 at river mile 825 to Pool 9 at river mile 648, paralleling spatial trends in the cadmium contamination of sediments in the reach downstream from the Twin Cities metropolitan area, reported in earlier studies; cadmium burdens in mayflies followed a similar spatial trend. Concentrations of mercury were much less variable, ranging from 44 to 102 ng/g dry weight in female mayflies and from 60 to 177 ng/g in males; concentrations and burdens were highest in mayflies collected at Pools 2, 20, 22, 25, and 27. Mercury concentrations in females decreased significantly with distance downstream from Pool 2 at river mile 825 to Pool 5A at river mile 728.5. Concentrations of mercury and cadmium in composite samples of female mayflies were not correlated, indicating dissimilar longitudinal patterns in concentrations of the two metals.(ABSTRACT TRUNCATED AT 250 WORDS)

Recent influxes of metals into Lake Pepin, a natural lake on the Upper Mississippi River.

The recent chronology of metal deposition was examined in Lake Pepin, a large natural lake on the Upper Mississippi River about 75 km downstream from the Minneapolis-St. Paul, Minnesota, metropolitan area. The lake, which has a high trapping efficiency for suspended sediments, serves as a sink for metals from industrial and domestic effluents discharged into the river. Sediment cores collected in 1981 from seven locations in the lake were analyzed for Cd, Cr, Cu, Ni, Pb, Zn, and Al (a reference element). Dating of a core with(137)Cs indicated that inputs of these metals increased markedly in the late 1950s, peaked in the early 1970s, and decreased in the late 1970s to 1981. Sediment enrichment factors decreased in the order Pb>Cd>Cu[Symbol: see text]Cr>Zn>Ni. The depth of the most highly contaminated strata in the core profiles decreased longitudinally from upstream to downstream-paralleling the upstreamto-downstream decrease in sedimentation rates. Changes in metal inputs to the lake would be most readily detected by analysis of sediments from the uppermost reaches, but the potential for release of sediment-associated metals to the water column is probably greatest in downstream reaches.