Susan W. Fisher

The Role of the Zebra Mussel, Dreissena polymorpha, In Contaminant Cycling: II. Zebra Mussel Contaminant Accumulation from Algae and Suspended Particles, and Transfer to the Benthic Invertebrate, Gammarus fasciatus

To determine the contribution of ingested material to zebra mussel contaminant accumulation, contaminant assimilation efficiencies (fraction of the total contaminant exposure that is accumulated into tissue, AE) from spiked algae and suspended sediment particles were measured for benzo(a)pyrene, the insecticide DDT, and selected polychlorinated biphenyl (PCB) congeners. Contaminant transfer from zebra mussel feces to the benthic invertebrate, Gammarus fasciatus, was determined by measuring AE from PCB contaminated mussel feces to gammarids. Further, mussel contaminant AE values coupled with physiological and environmental parameters were used in a steady-state model to examine the relative importance of the algal, suspended sediment, and water-borne exposure routes for a representative organochlorine compound, hexachlorobiphenyl (HCBP). The relative accumulation via the fecal and water exposure routes were modeled for gammarids. Mussel AE values for contaminant accumulation were greater from algae than from suspended sediments. Model estimates indicated that when contaminant concentrations in the water were near detection limits, dietary exposure was the primary route of contaminant accumulation (61.5% of the total contaminant concentration). Water was the most important route of contaminant exposure (89.5% of the total contaminant concentration) when contaminant concentrations in water were 10 times greater than the compound detection limit. Suspended sediment was the major dietary source of contaminants at all water concentrations. % AE for zebra mussel feces to gammarid transfer were high—79.0 and 89.4% for hexachlorobiphenyl and tetrachlorobiphenyl respectively—but not statistically different. Model estimates indicated that the dietary route of exposure was the primary source of PCB exposure for gammarids and indicated a potential for PCB biomagnification in the mussel-based detrital food chain. Results suggest that zebra mussels have the potential to change contaminant cycling in the Great Lakes by rerouting dissolved and paniculate bound contaminants through zebra mussel food chains with possible biomagnification in upper trophic levels.

The Role of the Zebra Mussel, Dreissena polymorpha, in Contaminant Cycling: I. The Effect of Body Size and Lipid Content on the Bioconcentration of PCBs and PAHs

The zebra mussel, Dreissena polymorpha, a recent invader to the Great Lakes, may influence contaminant cycling by bioconcentrating high levels of hydrophobic contaminants in its tissue. To better understand zebra mussel bioconcentration and ultimately, contaminant cycling, we measured bioconcentration factors (BCFs) and kinetic parameters for accumulation of polychlorinated biphenyl and poly cyclic aromatic hydrocarbon congeners for two size classes of mussels and for a pre-spawning (high lipid) and post-spawning (low lipid) mussel population. High lipid, pre-spawning mussels had greater BCFs and faster uptake kinetics for the highly hydrophobic compounds, i.e, hexachlorobiphenyl and benzo(a)pyrene, than the low lipid, post-spawning mussels. BCFs and uptake kinetics determined for the less hydrophobic compounds, i.e., tetrachlorobiphenyl and pyrene, were not measurably influenced by differences in lipid content. Small mussels (15 mm shell length) had higher BCFs and faster uptake kinetics for all compounds compared to larger (21 mm shell length) mussels. Contaminant elimination was not affected by size or differences in lipid levels. For both lipid levels and size classes of mussels, the BCFs were positively correlated with compound log octanohwater partition coefficient. Hence, the lipid affinity of a compound can be a good indicator of mussel contaminant accumulation. Potentially large contaminant concentration in zebra mussels may alter contaminant cycling in the Great Lakes by increasing contaminant transfer to mussel predators. Selective predation on small, pre-spawning (high lipid) mussels may present a greater hazard to predators than predation on larger, post-spawning (low lipid) mussels.

Trophic transfer and biotransformation of polychlorinated biphenyls in zebra mussel, round goby, and smallmouth bass in Lake Erie, USA

Trophic transfer of polychlorinated biphenyl (PCB) congeners in zebra mussels (Dreissena polymorpha), round gobies (Neogobius melanstomus), and smallmouth bass (Micropterus dolomieu) were assessed in four sites along the south shore of the west and central basin of Lake Erie (all sites were in OH, USA). Total PCB levels in smallmouth bass (1,091-1,520 ng/g wet weight) and round gobies (118-256 ng/g wet weight) were similar among sites despite a west-to-east decrease in total PCB concentrations in zebra mussels (29-97 ng/g wet weight). At all sites, PCB body burden increased three- to fivefold at each successive trophic level, suggesting biomagnification in this nonnative food chain. Whereas fish species were dominated by the hexachlorine homologue, zebra mussels were dominated by penta- and hexachlorine homologues; the average degree of chlorination of PCBs was 56.1% for zebra mussels, 60.4% for round goby, and 59.9% for smallmouth bass bodies. Predictive structure-activity relationships based on chemical characteristics, such as the octanol-water partition coefficient (log K(ow)), had little predictive power on bioaccumulation and biotransformation of PCB congeners because of nonlinearity, threshold relationships, and species-specific differences. Calculated trophic transfer for the smallmouth bass-round goby linkage was higher than for the round goby-zebra mussel linkage. Only when PCB congeners were grouped by chemical structure first (vicinal [adjacent] H-atom position in the phenyl ring) were linear relationships achieved. It appeared that the chemical group to which each congener belonged influenced biotransformation more than species-specific (round gobies vs smallmouth bass) differences. Biotic changes at midtrophic levels, such as exotic species invasions, may have an increasingly important role in determining pollutant cycling and hence pollutant residues in top predators.

Clearance and Processing of Algal Particles by Zebra Mussels (Dreissena polymorpha)

The exotic zebra mussel, Dreissena polymorpha Pallas, has become a dominant member of nearshore benthic communities in the Laurentian Great Lakes. Suspension-feeding bivalves such as the zebra mussel filter algal particles from the water column and either reject them as pseudofeces, digest them, or egest them asfeces. We used laboratory experiments to compare clearance and particle processing of two green algal species by zebra mussels. The effect of algal concentration on clearance rate of Chlamydomonas reinhardtii varied between large and small mussels. When mussels were fed Pandorina morum, clearance rate declined with increasing algal concentration. Mussel size affected clearance of C. reinhardtii but not P. morum. On a diet of P. morum, pseudofeces production was constant across algal concentrations. When fed C. reinhardtii, mussels increased pseudofeces production as algal concentration increased once a threshold was crossed. Below this threshold, no pseudofeces were produced. Measured clearance rates tended to be as high or higher than those previously reported, indicationg that incipient limiting concentrations vary with the types of particle processed. Absorption efficiencies were similar for both algal species. Our results show that particle processing by zebra mussels depends on the types of particles present in the water column and the size structure of the mussel population. To accurately determine the impacts of zebra mussels on the trophic structure of ecosystems and the cycling of contaminants, investigators must use realistic algal assemblages and account for the size structure of mussel populations.

Toxicity of Candidate Molluscicides to Zebra Mussels (Dreissena polymorpha) and Selected Nontarget Organisms

Many compounds have been marketed for control of zebra mussels (Dreissena polymorpha), but most compounds lack comparable toxicity data and have not been tested on nontarget organisms. We tested the toxicity of 18 chemicals to two sizes of zebra mussels, two nontarget fish (rainbow trout, Oncorhynchus mykiss and channel catfish, Ictalurus punctatus), and a unionid mussel (threehorn wartyback, Obliquaria reflexa) under standard conditions. Organisms were exposed to the chemicals for 48 h in “soft” reference water (pH 7.7, alkalinity 6 × 10−4 m/L (30 mg/L) as CaCO3, and total hardness 40 mg/L as CaCOj) at 17° C. Zebra mussels and unionid mussels were held in untreated reference water for another 48 h after exposure to measure delayed mortality. The LC50 values and 95% confidence intervals were compared among test organisms. Potassium chloride, Bayluscide (a registered molluscicide), and Clamtrol CT-1 (a poly quaternary ammonium compound) were the most selective chemicals tested against zebra mussels. They were two to three times more toxic to zebra mussels than to the nontarget species. Most of the remaining chemicals lacked the desired toxicity or were more toxic to fish than to zebra mussels.

The assimilation of contaminants from suspended sediment and algae by the zebra mussel, Dreissena polymorpha

Since their invasion into the Great Lakes, zebra mussels, Dreissena polymorpha, have increased the water clarity in Lake St. Clair and Lake Erie due to their extensive particle filtration. Because these particles contain sorbed contaminants, the potential for contaminant accumulation from both suspended sediment and algae were examined. Sediment or algae were dosed with selected radiolabeled polycyclic aromatic hydrocarbon congeners and/or hexachlorobiphenyl (HCBP). Assimilation efficiencies were measured and depended on food quality. Zebra mussels, 17 +/- 2 mm long, assimilated 58.3 +/- 13.5% of the pyrene and 44.7 +/- 5.8% of the benzo(a)pyrene (BaP) from sediment particles with a particle clearance rate of 493-897 ml/g tissue/h. However, assimilation efficiencies were 91.7 +/- 3.7% for pyrene, 91.9 +/- 1.4% for BaP, 96.6 +/- 1.4% for chrysene, and 97.7 +/- 0.5% for HCBP from suspended algae. Algal particle clearance rates for the mussels ranged from 47-143 ml/g tissue/h. Thus, zebra mussels efficiently accumulated non-polar contaminants sorbed to algae, while a smaller fraction of the sediment-associated contaminant was bioavailable. Furthermore, the contaminants sorbed onto suspended sediment particles were quickly removed from the water and deposited as pseudofeces. The pseudofeces production was positively correlated with filtration rate and suspended particle concentrations.

Lethal and sublethal body residues for PCB intoxication in the oligochaete, Lumbriculus variegatus

The oligochaete, Lumbriculus variegatus, was used to examine the utility of critical body residues in describing lethal and sublethal chronic endpoints during polychlorinated biphenyls (PCB) exposure. L. variegatus was exposed to four 14C-PCB congeners and 2,2-bis-(p-chlorophenyl)-1,1-dichloroethylene (DDE) on algal cells. Accumulation and resulting effects were monitored in 10-day acute and 35-day chronic exposures. L. variegatus was resistant to the acute lethal narcotic effects of these contaminants and no mortality was obtained in 10-day exposures. However, mortality that was significantly different from unexposed controls occurred for four compounds in 35-day assays; average body residues for chronic mortality were consistent among contaminants (0.88–1.35 mmol kg−1). Kinetic studies showed that failure to generate mortality in some exposures was due to rapid elimination. Mono-2-chlorobiphenyl, for instance, had a Kd of 0.22 h−1 which was seven to 44 times faster than for the other contaminants. Sublethal reductions in body mass and reproduction occurred at lower body residues than were needed to produce mortality (0.34–0.56 mmol kg−1). The consistency of the sublethal data suggests that they may offer a means of interpreting residue data for PCBs in the environment.

Influence of pH, temperature and sediment type on the toxicity, accumulation and degradation of parathion in aquatic systems

The effects of pH, temperature, and sediment on the toxicity and aquatic fate of parathion were investigated. Acute toxicity tests, accumulation and metabolism studies were conducted with midge larvae, Chironomus riparius, at pH values 4, 6, and 8 in water held at 10°C, 20°C, and 30°C, with and without sediment. Abiotic tests were also performed to determine the fate of parathion under various substrate conditions. Without exception, temperature was the most influential parameter tested. It altered both the toxicity and metabolism of parathion, at times increasing toxicity as much as 100-fold when the temperature increased from 10°C to 30°C. Sediment also influenced parathion toxicity and degradation, although to a lesser extent than temperature. Changes in pH had little influence on parathion toxicity or degradation. The results of these studies further emphasize the importance of abiotic factors on the environmental fate of xenobiotics.

Influence of Lipids on the Bioaccumulation and Trophic Transfer of Organic Contaminants in Aquatic Organisms

In aqueous systems, organisms are exposed to contaminants via multiple routes (Fig. 9.1). The extent of contaminant accumulation ultimately depends on the extent and mode of interaction with diverse contaminated media. The influence of lipids on contaminant uptake likewise varies according to the route by which the exposure takes place and the lipophilic character of the contaminant. Thus, it is necessary to clarify the environmental sources of contaminants for accumulation. The means by which contaminants, once accumulated, can be eliminated from an organism can also depend on organism lipid content. This elimination can be modified by the route, contaminant lipophilicity, and extent of contamination of the environmental compartment into which elimination occurs.

Changes in the toxicity of three pesticides as a function of environmental pH and temperature.

Accurate predictions of pesticide fate and toxicity in aqueous environments are hindered by lack of information on how site-specific water quality parameters affect the biological activity of these compounds. At present, there is a small data base which describes the effects of individual water quality parameters such as pH temperature and water hardness on pesticide fate. Indeed, where possible, the USEPA water quality criteria are based on pH or temperature adjusted measurements. However, there is little information on what influence simultaneous changes in two or more parameters in nature, it is important to have some estimate of what influence these parameters will exert when varied in concert. In the present study, the influence of simultaneous variation in pH and temperature on the toxicity of three pesticides, pentachlorophenol (PCP), aldicarb and benzene hexachloride (BHC), is considered.