Toxic Burdens of Freshwater Biofilms and Use as a Source Tracking Tool in Rivers and Streams.

Biofilms, composed of periphyton, bacteria, and organic detritus, are the base of the food web in many streams and rivers. This media adsorbs and actively sequesters organic and inorganic contaminants from the water column. Here, we demonstrate the utility of using the contaminant concentrations in the biofilm matrix as an environmental media in source tracking and understanding biological impacts at higher trophic levels. Physical partitioning of polychlorinated biphenyl (PCB) and polybrominated diphenyl ether congeners is the dominant mode of uptake from water to biofilm and bioaccumulation factor: log Kow relationships suggest that PCB uptake is often near equilibrium between log Kow 5-7. We show that the concentrations of metals in biofilms are more effective at delineating and recording spatial and temporal differences in metal inputs than bed sediments and water samples. The burden of metals in the biofilm matrix explained adverse impacts and variability in periphyton metrics and ecological integrity in macroinvertebrates. This work provides new insights into the partitioning of organic chemicals onto biofilms and shows clear linkages between metals in the biofilm matrix and ecological health of invertebrates that depend on biofilms as a food source.

Effects of chronic copper exposure on the nutritional composition of Hyalella azteca.

The toxicity of dietborne metals currently is a topic of high interest in aquatic toxicology. We hypothesized that, in addition to causing direct physiological effects when ingested by organisms, dietborne metals might also cause indirect foodweb effects. One such indirect effect might be alteration of the nutritional content of prey, leading to decreased growth and (or) survival of consumers. Because dietborne and waterborne metal exposures usually occur concurrently in aquatic ecosystems, we exposed two generations of a representative grazer species-the freshwater amphipod Hyalella azteca-to dietborne copper (Cu) concurrent with waterborne Cu in the laboratory for a total of 27 days (first generation) and 45-57 days (second generation). The aqueous Cu concentrations were 0.0099 (control), 0.054 and 0.11 microM (0.6, 3.4 and 7.0 microg Cu per l, respectively) at 24 degrees C, pH 7.5-8.3, alkalinity of approximately 3 mEq/l and hardness of approximately 4 mEq/l; whereas the dietborne Cu exposures were via biofilm growing on cotton gauze in the same exposure aquaria. In a preliminary test, we demonstrated that the highest Cu concentrations were at the threshold for adversely affecting survival and reproduction. In the two-generation test, first- and second-generation amphipods exposed to the intermediate and high aqueous Cu concentrations accumulated significantly higher amounts of Cu than control amphipods. However, none of the traditional nutritional composition categories (protein, total lipid, ash and 'other') differed among the treatments. The only significant difference in nutritional composition was an elevated concentration of linolenic acid (18:3 n-3) in the second-generation amphipods exposed to 0.054 microM Cu.

Whole-body accumulation of copper predicts acute toxicity to an aquatic oligochaete (Lumbriculus variegatus) as pH and calcium are varied.

We tested the hypothesis that whole-body accumulation of Cu at 50% mortality (i.e. the median lethal accumulation, LA50 value) in a freshwater oligochaete (Lumbriculus variegatus) is constant across a wide range of water quality, whereas the LC50 values of Cu(total) and the cupric ion (Cu(2+)) in solution are not. We exposed the worms in intermittent-flow, water-only chambers to a series of Cu concentrations at a variety of combinations of pH and water hardness (pH 6.5, 7.5 and 8.5 crossed with hardnesses of 0.5, 2, 4, 6 and 15 mEql(-1)) at 17-20 degrees C. In addition to monitoring mortality at 48 h, we determined whole-body Cu uptake in half of the replicate chambers at 6 h. LC50 values of Cu(total) and Cu(2+) increased as water hardness increased, as expected from traditional LC50 vs. hardness regressions. Moreover, LC50 values of Cu(total) remained approximately constant and LC50 values of Cu(2+) decreased considerably as pH increased, as expected from principles of cation competition and binding by inorganic ligands. However, LA50 values of Cu(body) remained approximately constant (0.17-0.34 micromol Cug(-1) dry wt.) in all pH x hardness combinations. Thus, consistent with the biotic-ligand model, Cu accumulation might be a constant predictor of acute mortality to L. variegatus whereas aqueous Cu concentrations are not.