Jason B. Belden

Toxicity of fluoroquinolone antibiotics to aquatic organisms

Toxicity tests were performed with seven fluoroquinolone antibiotics, ciprofloxacin, lomefloxacin, ofloxacin, levofloxacin, clinafloxacin, enrofloxacin, and flumequine, on five aquatic organisms. Overall toxicity values ranged from 7.9 to 23,000 microg/L. The cyanobacterium Microcystis aeruginosa was the most sensitive organism (5-d growth and reproduction, effective concentrations [EC50s] ranging from 7.9 to 1,960 microg/L and a median of 49 microg/L), followed by duckweed (Lemna minor, 7-d reproduction, EC50 values ranged from 53 to 2,470 microg/L with a median of 106 microg/L) and the green alga Pseudokirchneriella subcapitata (3-d growth and reproduction, EC50 values ranged from 1,100 to 22,700 microg/L with a median 7,400 microg/L). Results from tests with the crustacean Daphnia magna (48-h survival) and fathead minnow (Pimephales promelas, 7-d early life stage survival and growth) showed limited toxicity with no-observed-effect concentrations at or near 10 mg/L. Fish dry weights obtained in the ciprofloxacin, levofloxacin, and ofloxacin treatments (10 mg/L) were significantly higher than in control fish. The hazard of adverse effects occurring to the tested organisms in the environment was quantified by using hazard quotients. An estimated environmental concentration of 1 microg/L was chosen based on measured environmental concentrations previously reported in surface water; at this level, only M. aeruginosa may be at risk in surface water. However, the selective toxicity of these compounds may have implications for aquatic community structure.

Challenges in regulating pesticide mixtures

This paper introduces the field of mixture toxicity and the challenges in regulating pesticide mixtures. Even though pesticides are unique chemical stressors designed to have biological activity that can affect a number of nontarget species, they are intentionally placed into the environment in large quantities. Currently, methods and terminology for evaluating mixture toxicity are poorly established. The most common approach used is the assumption of additive concentration, with the concentrations adjusted for potency to a reference toxicant. Using this approach, the joint action of pesticides that have similar chemical structures and modes of toxic action can be predicted. However, this approach and other modeling techniques often provide little insight into the observed toxicity produced by mixtures of pesticides from different classes. Particularly difficult to model are mixtures that involve a secondary toxicant that changes the toxicokinetics of a primary toxicant. This may result in increased activation or a change in the persistence of the primary toxicant within the organism and may be responsible for a several-fold increase or decrease in toxicity. At present, the ecological effects caused by mixtures of pesticides are given little consideration in the regulatory process. However, mixtures are being considered in relation to human health in the pesticide registration process, setting a precedent that could be followed for ecological protection. Additionally, pesticide mixtures may be regulated through toxicity testing of surface water under the Clean Water Act. The limits of our basic knowledge of how mixtures interact are compromising both these avenues for regulating mixtures. We face many challenges to adequately protecting the environment from mixture toxicity; these challenges include understanding the interactions of toxicants within an organism, identifying the mixtures that most commonly occur and cause adverse effects, and developing a regulatory structure capable of minimizing environmental impacts.

Occurrence and potential toxicity of pyrethroids and other insecticides in bed sediments of urban streams in central Texas.

Despite heavy insecticide usage in urban areas, only a few studies have investigated the impact of current-use insecticides on benthic invertebrates in urban streams. The objective of this study was to measure the presence and concentration of current-use pesticides in sediments of residential streams in central Texas. Additionally, toxicity of these sediments to Hyalella azteca was evaluated. Sediment samples were collected from several sites in urban streams over the course of a year, of which, 66% had greater than one toxic unit (TU) of insecticide. Bifenthrin was the greatest contributor accounting for 65% of the TUs, and sediment toxicity to H. azteca correlated with the magnitude of total insecticides and bifenthrin TUs. The results of this study further raise concerns over the environmental consequences posed by many current-use insecticides, especially pyrethroids, in urban settings.

Joint toxicity of chlorpyrifos and esfenvalerate to fathead minnows and midge larvae

The joint toxicity of esfenvalerate and chlorpyrifos to the fathead minnow (Pimephales promelas) and the aquatic midge larvae (Chironomus tentans) was determined using comparisons to independent action (IA) and concentration addition (CA) models. Equipotent mixtures of the two insecticides were used for initial testing of both species. A secondary study evaluating the effects of low-level chlorpyrifos on esfenvalerate toxicity also was performed. For fathead minnows, the equipotent mixture and the low-level chlorpyrifos exposure resulted in toxicity greater than that predicted by either model. In both studies, however, the observed concentrations causing 50% effect (EC50) were within a factor of two of the values predicted by the CA model. For midges, the observed EC50s were similar to the values predicted by the CA model, whereas the IA model slightly underpredicted toxicity. The observance of toxicity that was not predicted by either of the conceptual models tested likely results from a toxicokinetic interaction occurring between the toxicants.

Acute toxicity of fungicide formulations to amphibians at environmentally relevant concentrations

Fungicide use on row crops is increasing dramatically due to promotion of these products for general plant health and increased yield even during low disease pressure. These fungicides are applied aerially, which may lead to amphibian exposure within fields or in nearby habitat. Exposure to three of these fungicides at environmentally relevant conditions resulted in mortality for Bufo tadpoles and juveniles for two of the fungicides. Headline®, the most commonly used on row crops, resulted in >50% mortality for juveniles at corn label application rates and 100% mortality for tadpoles at one-tenth the label rate for corn. Stratego® killed 40% of exposed tadpoles on average at the corn label rate, but only 7% of the juveniles. Overall, Quilt® appeared less toxic than the other fungicides, resulting in 7 to 10% mortality of tadpoles and 4 to 22% mortality of juveniles at all concentrations (from 0.1× to 10× label rate). These fungicides, especially Headline, may pose a major hazard for amphibians exposed as tadpoles and/or juveniles at environmentally relevant concentrations.

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.

Bioaccumulation and trophic transfer of polychlorinated biphenyls by aquatic and terrestrial insects to tree swallows (Tachycineta bicolor)

Insectivorous passerines often bioaccumulate polychlorinated biphenyls (PCBs) via trophic transfer processes. Tree swallows (Tachycineta bicolor) frequently are used for estimating PCB bioaccumulation, yet the focus on specific trophic links between contaminated sediment and bird has been limited. Bioaccumulation of PCBs from sediment to tree swallows was examined with focus on trophic pathways by simultaneously examining PCBs in emergent aquatic and terrestrial insects and gut contents of nestlings. Total PCB concentrations increased from sediment (123.65 +/- 15.93 microg/kg) to tree swallow nestlings (2,827.76 +/- 505.67 microg/kg), with emergent aquatic insects, terrestrial insects, and gut content samples having intermediate concentrations. Biota-sediment accumulation factors (BSAFs) varied among congeners for tree swallow nestlings and for male and female Chironomus spp. For nestlings, the highest BSAF was for the mono-ortho-substituted congener 118. Nestling biomagnification values were similar for gut contents and female Chironomus spp., suggesting this diet item may be the main contributor to the overall PCB transfer to nestlings. However, gut content samples were highly variable and, on a PCB congener pattern basis, may have been influenced by other taxa, such as terrestrial insects. Considering dietary plasticity of many insectivorous birds, the present study suggests that a variety of potential food items should be considered when examining PCB accumulation in insectivorous passerines.

Identification and evaluation of pyrethroid insecticide mixtures in urban sediments

Organochlorine, organophosphorous, and pyrethroid insecticides frequently have been detected together as mixtures in stream sediments. To simplify mixture analyses, additive toxic responses usually are assumed but rarely are confirmed, especially for compounds with similar modes of action. The first objective of the present study was to screen a database of 24 different pesticides and 94 urban-stream sediment samples collected throughout central and northern California (USA) to identify compounds and partial mixtures that dominated sample toxicity to Hyalella azteca. Pyrethroids and chlorpyrifos were the most toxicologically relevant compounds in terms of detection frequency, contribution to overall sample toxicity, and co-occurrence in the most common mixture patterns. Organochlorine insecticides were the least toxicologically relevant compounds, with only a small percentage of samples exceeding predefined screening values. The second objective was to confirm that mixtures of type I and type II pyrethroids display additive responses. Ten-day sediment toxicity tests of binary pesticide mixtures were conducted using H. azteca as the test organism. Observed dose-response curves were compared to those predicted from concentration-addition and independent-action models. Model deviation ratios (MDRs) were calculated at the median effect level to quantify the magnitudes of deviation between observed and predicted curves. Whereas the concentration-addition model adequately predicted toxicity for all the pyrethroid mixtures (MDRs within a factor of two), dose-response values deviated from additivity enough to warrant further investigation.

Assessment of the Effects of Farming and Conservation Programs on Pesticide Deposition in High Plains Wetlands

We examined pesticide contamination in sediments from depressional playa wetlands embedded in the three dominant land-use types in the western High Plains and Rainwater Basin of the United States including cropland, perennial grassland enrolled in conservation programs (e.g., Conservation Reserve Program [CRP]), and native grassland or reference condition. Two hundred and sixty four playas, selected from the three land-use types, were sampled from Nebraska and Colorado in the north to Texas and New Mexico in the south. Sediments were examined for most of the commonly used agricultural pesticides. Atrazine, acetochlor, metolachlor, and trifluralin were the most commonly detected pesticides in the northern High Plains and Rainwater Basin. Atrazine, metolachlor, trifluralin, and pendimethalin were the most commonly detected pesticides in the southern High Plains. The top 5-10% of playas contained herbicide concentrations that are high enough to pose a hazard for plants. However, insecticides and fungicides were rarely detected. Pesticide occurrence and concentrations were higher in wetlands surrounded by cropland as compared to native grassland and CRP perennial grasses. The CRP, which is the largest conservation program in the U.S., was protective and had lower pesticide concentrations compared to cropland.

Fluoxetine alters adult freshwater mussel behavior and larval metamorphosis.

We used acute and partial-lifecycle tests to examine the effects of the pharmaceutical fluoxetine on freshwater mussels (Unionida). In acute tests lasting 24-48 h, we determined median effective concentrations (EC50s) for fluoxetine with larval (glochidia viability) and juvenile (survival) life-stages of fatmucket (Lampsilis siliquoidea) and black sandshell (Ligumia recta). In a 28-d behavioral test we exposed brooding adult female wavy-rayed lampmussels (Lampsilis fasciola) to 0.37 and 29.3 μg/L fluoxetine to determine effects on adult behavior (foot protrusion, mantle lure display and glochidia parturition). We also assessed the effects of 24-h exposure of 1 and 100 μg/L fluoxetine on glochidia viability duration and metamorphosis success for the wavy-rayed lampmussel. Fluoxetine EC50s ranged from 62 μg/L for juveniles (96 h) to 293 μg/L for glochidia (24 h). In adults, statistically significant increases were observed in foot protrusion at 0.37 and 29.3 μg/L fluoxetine and lure display rates at 29.3 μg/L; glochidia parturition was not significantly affected at any test concentration. Twenty-four hour exposure of glochidia to fluoxetine did not affect viability duration, but likelihood of metamorphosis to the juvenile stage significantly increased with 1 and 100 μg/L treatments. Our results demonstrated effects of fluoxetine to unionid mussels at concentrations less than previously reported and approaching concentrations measured in surface waters.