Lance J. Schuler

Effects of the antibiotic ciprofloxacin on stream microbial communities and detritivorous macroinvertebrates

Microbial communities play an important role in stream ecosystem processes, such as breakdown of senescent leaf litter, and as a primary nutritional source for detritivorous macroinvertebrates. Antibiotics may affect stream microbial communities and associated ecosystem processes, especially because recent stream and river monitoring programs have indicated the presence of antibiotics downstream of wastewater treatment plants. In the current study, effects of chronic exposure to the fluoroquinolone antibiotic ciprofloxacin (Cipro) were examined on stream microbial community-level physiological profiles and growth indices of detritivorous amphipods (Gammarus spp.) and caddisflies (Lepidostoma liba). Microcosm experiments were conducted using stream sediments and water, senesced leaf material (Acer saccharum), and macroinvertebrates. A shift in function of leaf-associated microbial communities (based on carbon source utilization) was observed for samples exposed to 100 microg/L of Cipro for 12 d compared to control and treatments exposed to 1 and 10 microg/L of Cipro. This was attributable to carbohydrate substrates, which had 2.7- to 3.5-fold lower microbial respiration than the lower concentrations and control (p < 0.001). For detritivores, Gammarus spp. condition index did not differ among control, 0.1, and 1.0 microg/L treatments after 30-d exposures (p > 0.05). Similarly, L. liba growth rate did not vary among control, 10, and 100 microg/L treatments after 45-d exposures (p > 0.05). These results suggest that Cipro may affect leaf-associated microbial communities, but at concentrations four orders of magnitude above those detected in streams. However, effects of the antibiotic on growth and condition of detritivores were not observed. Future work should focus on identifying specific changes in stream microbial communities as a result of Cipro exposure and impacts on other aquatic species.

Joint toxicity of fluoranthene and pentachlorobenzene to Hyalella azteca and Chironomus dilutus.

Nonpolar organic chemicals such as polycyclic aromatic hydrocarbons and chlorobenzenes are expected to act additively when exposed as a mixture. The present study examined the toxicity of fluoranthene (FLU) and pentachlorobenzene (PCBz) individually and in a binary mixture using the whole-body residue as the dose metric. Body residues were based on the toxic equivalent body residue, which included the parent compound plus the organically extractable metabolites for FLU and the parent compound only for PCBz. Using a toxic unit (TU) approach, the binary mixtures of FLU and PCBz following 4- and 10-d water-only exposures acted additively. The lethal residue (LR50) values for mixtures of the compounds for Hyalella azteca were 1.26 (1.19-1.33) TU and 1.27 (1.20-1.34) TU for 4- and 10-d exposures, respectively. For Chironomus dilutus, the 4-d and 10-d values were 0.93 (0.90-0.97) TU and 1.01 (0.96-1.06) TU. Additionally, the total molar sum of PCBz and FLU whole-body residues in a mixture were compared to residues from single compound exposures. For both species tested, the LR50 values based on the total molar sum fell within the range of those determined from the single compound tests; providing additional support for molar additivity for nonpolar narcotic compounds. Assuming that residue-effects data among narcotic compounds (e.g., LR50) are similar, applying the molar sum methodology to narcotic compounds in tissues determined from routine biomonitoring programs and risk specific sampling may be a valuable tool to assess potential effects to biota in the field.

Response spectrum of pentachlorobenzene and fluoranthene for Chironomus tentans and Hyalella azteca

The whole-body residues of pentachlorobenzene (PCBz) and fluoranthene (FLU) in Hyalella azteca and Chironomus tentans were determined for a variety of chronic sublethal effects. The endpoints evaluated for H. azteca included 28-d growth and survival and 42-d growth, survival, and reproduction. Adverse effects to C. tentans also were determined at multiple endpoints including 10-d growth, cumulative pupation and emergence, and reproduction. The lowest-observed-effect residue (LOER) based on whole-body residues associated with growth was consistent between compounds and species tested with concentrations ranging from 0.17 to 0.33 micromol/g. For H. azteca, the most sensitive endpoints were growth at 0.23 micromol/g and reproduction at 0.11 micromol/g for PCBz and FLU, respectively. For C. tentans, the most sensitive endpoints were emergence, development and reproduction at 0.02 micromol/g, and development and reproduction at 0.15 micromol/g for PCBz and FLU, respectively. Compared to residues associated with acute lethality, the most sensitive sublethal endpoints were approximately 4 and 60 times lower for PCBz and FLU, respectively. The relative consistency of the sublethal endpoints suggests that body residues can be a valuable tool to evaluate bioaccumulation data as part of a risk assessment to predict adverse effects to biota.

Response spectrum of fluoranthene and pentachlorobenzene for the fathead minnow (Pimephales promelas)

Internal body residue has been recognized as a potential dose metric for toxicological assessments. This relationship between body residue and biological effects, including both lethal and sublethal effects, is critically important for determining environmental quality in risk assessments. The present study identified the toxic equivalent body residues for fluoranthene (FLU) and pentachlorobenzene (PCBz) associated with mortality, reduced growth, and decreased hatchability in the fathead minnow. The toxic equivalent body residue was defined as the total of the parent compound and the organically extractable metabolites for FLU and of the parent compound only for PCBz, because no biotransformation was measurable. The lethal body residues corresponding to 50% mortality were 0.80 and 1.26 micromol/g wet weight for FLU and PCBz, respectively. As expected, residues associated with sublethal effects generally are 2- to 40-fold lower than the lethal residues for FLU and PCBz. Juvenile fish growth was the most sensitive endpoint examined for both compounds. The maximum allowable toxicant residues were 0.02 and 0.43 micromol/g wet weight for FLU and PCBz, respectively. The information collected from the present study will permit a greater understanding of residue-response relationships, which will be useful in risk assessments.

Aquatic Risk Assessment of Metals in Sediment from South Florida Canals

A major watershed restoration effort is underway in south Florida, yet there are significant gaps in scientific information on exposure and risks of contaminants to its natural resources. We conducted a two-tier aquatic screening-level ecological risk assessment for metals that were monitored in sediment at 32 sampling sites in south Florida freshwater canals from 1990–2002. For tier 1, the chemicals (or metals) of potential ecological concern (COPECs) were identified as arsenic, cadmium, chromium, copper, lead, nickel and zinc based on their exceedences of Florida sediment quality guidelines at 10 sites. For tier 2, we used a probabilistic risk assessment method to compare distributions of predicted pore water exposure concentrations of seven metal COPECs with distributions of species response data from laboratory toxicity tests to quantify the likelihood of risk. The overlap of pore water concentrations (90th centile for exposure) for metal COPECs and the effects distributions for arthropods (10th centile of LC50s) and all species (10th centile of chronic NOECs) were used as a measure of potential acute and chronic risks, respectively. Arsenic (25%) in the Holey Land tracts, in Broward County north of Everglades National Park (ENP), and chromium (25%) in the C-111 freshwater system, at the east boundary of ENP, were the most frequently detected COPECs in sediment. Antimony (6%), zinc (6%) and lead (5%) were the least frequently detected COPECs in sediment. The 90th centile concentrations for bulk sediment were highest for zinc (at S-178) and lead (at S-176) in the C-111system. The 90th centile concentration for pore water exposure was highest for arsenic in the Holey Land tracts and lowest for cadmium and chromium. The estimated acute 10th centile concentration for effects was lowest for copper and arthropods. The probabilities of pore water exposures of copper exceeding the estimated acute 10th centile concentration from the species sensitivity distributions (SSD) of acute toxicity data (for arthropods) were 57 and 100% for copper at S-177 and S-178 in the C-111 system, respectively. The probability of pore water exposures of copper exceeding the estimated NOEC 10th centile concentration from the SSD of chronic toxicity data (for all species) was 93 and 100% for copper at S-177 and S-178, respectively. Uncertainties in exposure and effects analysis and risk characterization are identified and discussed. The study presents a straightforward approach to estimate exposure and potential risks of metals detected in sediment from south Florida canals.

Congener-specific egg contribution of polychlorinated biphenyls to nestlings in two passerine species.

Quantifying polychlorinated biphenyl (PCB) residues in nestlings of avian species is a common method for assessing trophic transfer and risk at PCB-contaminated sites. The proportion of nestling PCB mass due to maternal transfer is often accounted for by subtracting total PCB mass in eggs from nestlings. However, variation in physicochemical properties and metabolism among congeners may lead to differences between egg contribution based on total PCBs and dioxin-like congeners. We examined congener-specific variation in contribution of PCBs from eggs to nestlings in tree swallows and European starlings. Egg contribution of total PCB mass was 14.3 and 16.2%, respectively, whereas contribution based on dioxin-like congeners was 14.8 and 13.6%, respectively. These data suggest that using total PCB mass in eggs to adjust estimates of PCB accumulation in nestlings may not reflect patterns for dioxin-like congeners, potentially over or under-estimating the risk of toxicity of PCBs.