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At least 505 records · Page 28Linked to original sources
USGS2004

Mercury accumulation and loss in mallard eggs

Female mallards ( Anas platyrhynchos ) were fed diets containing 5, 10, or 20 ppm mercury as methylmercury chloride. One egg was collected from each bird before the start of the mercury diets and 15 eggs were collected from each bird while it was being fed mercury. The mercury diets were then replaced by uncontaminated diets, and each female was allowed to lay 29 more eggs. Mercury levels in eggs rose to about 7,18, and 35 ppm wet-weight in females fed 5,10, or 20 ppm mercury, respectively. Mercury levels fell to about 0.16,0.80, and 1.7 ppm in the last egg laid by birds that had earlier been fed 5, 10, or 20 ppm mercury, respectively. Higher concentrations of mercury were found in egg albumen than in yolk, and between 95 and 100% of the mercury in the eggs was in the form of methylmercury.

Environmental Toxicology and Chemistry↗
USGS2004

Time-dependent lethal body residues for the toxicity of pentachlorobenzene to Hyalella azteca

The study examined the temporal response of Hyalella azteca to pentachlorobenzene (PCBZ) in water-only exposures. Toxicity was evaluated by calculating the body residue of PCBZ associated with survival. The concentration of PCBZ in the tissues of H. azteca associated with 50% mortality decreased from 3 to 0.5 μmol/g over the temporal range of 1 to 28 d, respectively. No significant difference was observed in the body residue calculated for 50% mortality when the value was determined using live or dead organisms. Metabolism of PCBZ was not responsible for the temporal response because no detectable PCBZ biotransformation occurred over an exposure period of 10 d. A damage assessment model was used to evaluate the impact and repair of damage by PCBZ on H. azteca. The toxicokinetics were determined so that the temporal toxicity data could be fit to a damage assessment model. The half-life calculated for the elimination of PCBZ averaged approximately 49 h, while the value determined for the half-life of damage repair from the damage assessment model was 33 h.

Environmental Toxicology and Chemistry↗
USGS2004

Importance of equilibration time in the partitioning and toxicity of zinc in spiked sediment bioassays

The influences of spiked Zn concentrations (1–40 μmol/g) and equilibration time (˜ 95 d) on the partitioning of Zn between pore water (PW) and sediment were evaluated with estuarine sediments containing two levels (5 and 15 μmol/g) of acid volatile sulfides (AVS). Their influence on Zn bioavailability was also evaluated by a parallel, 10‐d amphipod ( Leptocheirus plumulosus ) mortality test at 5, 20, and 85 d of equilibration. During the equilibration, AVS increased (up to twofold) with spiked Zn concentration ([Zn]), whereas Zn‐simultaneously extracted metals ([SEM]; Zn with AVS) remained relatively constant. Concentrations of Zn in PW decreased most rapidly during the initial 30 d and by 11‐ to 23‐fold during the whole 95‐d equilibration period. The apparent partitioning coefficient ( K pw , ratio of [Zn] in SEM to PW) increased by 10‐ to 20‐fold with time and decreased with spiked [Zn] in sediments. The decrease of PW [Zn] could be explained by a combination of changes in AVS and redistribution of Zn into more insoluble phases as the sediment aged. Amphipod mortality decreased significantly with the equilibration time, consistent with decrease in dissolved [Zn]. The median lethal concentration (LC50) value (33 μM) in the second bioassay, conducted after 20 d of equilibration, was twofold the LC50 in the initial bioassay at 5 d of equilibration, probably because of the change of dissolved Zn speciation. Sediment bioassay protocols employing a short equilibration time and high spiked metal concentrations could accentuate partitioning of metals to the dissolved phase and shift the pathway for metal exposure toward the dissolved phase.

Environmental Toxicology and Chemistry↗
USGS2004

Concentrations of metals and trace elements in blood of spectacled and king eiders in northern Alaska, USA

In 1996, we measured concentrations of arsenic, barium, cadmium, lead, mercury, and selenium in blood of adult king (Somateria spectabilis) and spectacled (Somateria fischeri) eiders and duckling spectacled eiders from northern Alaska, USA. Concentrations of selenium exceeded background levels in all adults sampled and 9 of 12 ducklings. Mercury was detected in all adult spectacled eiders and 5 of 12 ducklings. Lead concentrations were above the clinical toxicity threshold in one duckling (0.64 ppm) and two adult female spectacled eiders (0.54 and 4.30 ppm). Concentrations of cadmium and mercury varied between species; barium, cadmium, mercury, and selenium varied between sexes. In female spectacled eiders, mercury concentrations increased during the breeding season and barium and selenium levels decreased through the breeding season. Selenium declined at 2.3 ± 0.9% per day and levels were lower in spectacled eiders arriving to the breeding grounds in northern Alaska than in western Alaska. The variation in selenium levels between breeding areas may be explained by differences in timing and routes of spring migration. Most trace elements for which we tested were not at levels currently considered toxic to marine birds. However, the presence of mercury and elevated lead in ducklings and adult female spectacled eiders suggests these metals are available on the breeding grounds.

Alaska↗
USGS2004

Linking metal bioaccumulation of aquatic insects to their distribution patterns in a mining-impacted river

Although the differential responses of stream taxa to metal exposure have been exploited for bioassessment and monitoring, the mechanisms affecting these responses are not well understood. In this study, the subcellular partitioning of metals in operationally defined metal-sensitive and detoxified fractions were analyzed in five insect taxa. Samples were collected in two separate years along an extensive metal contamination gradient in the Clark Fork River (MT, USA) to determine if interspecific differences in the metal concentrations of metal-sensitive fractions and detoxified fractions were linked to the differences in distributions of taxa relative to the gradient. Most of the Cd, Cu, and Zn body burdens were internalized and potentially biologically active in all taxa, although all taxa appeared to detoxify metals (e.g., metal bound to cytosolic metal-binding proteins). Metal concentrations associated with metal-sensitive fractions were highest in the mayflies Epeorus albertae and Serratella tibialis , which were rare or absent from the most contaminated sites but occurred at less contaminated sites. Relatively low concentrations of Cu were common to the tolerant taxa Hydropsyche spp. and Baetis spp., which were widely distributed and dominant in the most contaminated sections of the river. This suggested that distributions of taxa along the contamination gradient were more closely related to the bioaccumulation of Cu than of other metals. Metal bioaccumulation did not appear to explain the spatial distribution of the caddisfly Arctopsyche grandis , considered to be a bioindicator of metal effects in the river. Thus, in this system the presence/absence of most of these taxa from sites where metal exposure was elevated could be differentiated on the basis of differences in metal bioaccumulation.

Montana↗
USGS2004

Blarina brevicauda as a biological monitor of polychlorinated biphenyls: Evaluation of hepatic cytochrome p450 induction

We assessed the value of short-tailed shrews ( Blarina brevicauda ) as a possible biomonitor for polychlorinated biphenyl pollution through measurement of the induction of hepatic cytochrome P450 and associated enzyme activities. First, we checked the inducibility of four monooxygenases (benzyloxyresorufin-O-dealkylase [BROD], ethoxyresorufin-O-dealkylase [EROD], methoxyresorufin-O-dealkylase [MROD], and pentoxyresorufin-O-dealkylase [PROD]) by measuring the activity of these enzymes in hepatic microsomes prepared from shrews injected with $-naphthoflavone ($NF) or phenobarbital (PB), typical inducers of cytochrome P4501A (CYP1A) and CYP2B enzyme families, respectively. Enzyme activity was induced in shrews that received $NF but not in shrews that received PB; PROD was not induced by either exposure. Later, shrews were exposed to a mixture of polychlorinated biphenyls (PCBs) (Aroclor 1242:1254, in 1:2 ratio) at 0.6, 9.6, and 150 ppm in food, for 31 d. Induction in these shrews was measured by specific enzyme activity (BROD, EROD, and MROD) in hepatic microsomes, by western blotting of solubilized microsomes against antibodies to CYP1A or CYP2B, and by duration of sodium pentobarbital-induced sleep. These three CYP enzymes were induced in shrews by PCBs at similar levels of exposure as in cotton rat ( Sigmodon hispidus ). Neither sleep time nor the amount of CYP2B family protein were affected by PCB exposure. Blarina brevicauda can be a useful biomonitor of PCBs that induce CYP1A, especially in habitats where they are the abundant small mammal.

Environmental Toxicology and Chemistry↗
USGS2004

Modeling selenium bioaccumulation through arthropod food webs in San Francisco Bay, California, USA

Trophic transfer is the main process by which upper trophic level wildlife are exposed to selenium. Transfers through lower levels of a predator's food web thus can be instrumental in determining the threat of selenium in an ecosystem. Little is known about Se transfer through pelagic, zooplankton‐based food webs in San Francisco Bay ([SFB], CA, USA), which serve as an energy source for important predators such as striped bass. A dynamic multipathway bioaccumulation model was used to model Se transfer from phytoplankton to pelagic copepods to carnivorous mysids ( Neomysis mercedis ). Uptake rates of dissolved Se, depuration rates, and assimilation efficiencies (AE) for the model were determined for copepods and mysids in the laboratory. Small (73‐250 μm) and large (250‐500 μm) herbivorous zooplankton collected from SFB ( Oithona/Limnoithona and Acartia sp.) assimilated Se with similar efficiencies (41‐52%) from phytoplankton. Mysids assimilated 73% of Se from small herbivorous zooplankton; Se AE was significantly lower (61%) than larger herbivorous zooplankton. Selenium depuration rates were high for both zooplankton and mysids (12‐25% d −1 ), especially compared to bivalves (2‐3% d −1 ). The model predicted steady state Se concentrations in mysids similar to those observed in the field. The predicted concentration range (1.5‐5.4 μg g −1 ) was lower than concentrations of 4.5 to 24 μg g −1 observed in bivalves from the bay. Differences in efflux between mysids and bivalves were the best explanation for the differences in uptake. The results suggest that the risk of selenium toxicity to predators feeding on N. mercedis would be less than the risk to predators feeding on bivalves. Management of selenium contamination should include food webs analyses to focus on the most important exposure pathways identified for a given watershed.

California↗
USGS2004

Pesticides in mountain yellow-legged frogs (Rana muscosa) from the Sierra Nevada Mountains of California, USA

In 1997, pesticide concentrations were measured in mountain yellow-legged frogs (Rana muscosa) from two areas in the Sierra Nevada Mountains of California, USA. One area (Sixty Lakes Basin, Kings Canyon National Park) had large, apparently healthy populations of frogs. A second area (Tablelands, Sequoia National Park) once had large populations, but the species had been extirpated from this area by the early 1980s. The Tablelands is exposed directly to prevailing winds from agricultural regions to the west. When an experimental reintroduction of R. muscosa in 1994 to 1995 was deemed unsuccessful in 1997, the last 20 (reintroduced) frogs that could be found were collected from the Tablelands, and pesticide concentrations in both frog tissue and the water were measured at both the Tablelands and at reference sites at Sixty Lakes. In frog tissues, dichlorodiphenyldichloroethylene (DDE) concentration was one to two orders of magnitude higher than the other organochlorines (46 ?? 20 ng/g wet wt at Tablelands and 17 ?? 8 Sixty Lakes). Both ??-chlordane and trans-nonachlor were found in significantly greater concentrations in Tablelands frog tissues compared with Sixty Lakes. Organophosphate insecticides, chlorpyrifos, and diazinon were observed primarily in surface water with higher concentrations at the Tablelands sites. No contaminants were significantly higher in our Sixty Lakes samples.

Environmental Toxicology and Chemistry↗
USGS2004

Profiles of polychlorinated biphenyl congeners, organochlorine pesticides and butlyns in southern sea otters and their prey

Concentrations of organochlorine pesticides, polychlorinated biphenyl (PCB)congeners, and butyltins were measured in sea otters and selected prey species (invertebrates) collected from the California (USA) coast. Polychlorinated biphenyls, DDTs (sum of p,p ′-dichlorodiphenyldichloroethylene [ p,p -DDE], p,p ′-dichlorodiphenyldichloroethane [ p,p -DDD], and p,p ′-DDT), and butyltins were the major contaminants found in sea otters and their prey. Lipid-normalized concentrations of PCBs and DDT in sea otter livers were 60- and 240-fold greater than those found in the prey. Great biomagnification of PCBs and DDT in sea otters is suggested to result from their high per-capita intake of diet compared with those of other marine mammals. Profiles of PCB congeners in sea otters and prey species suggest a great capacity of sea otters to biotransform lower-chlorinated congeners. Sea otters seem to possess a greater ability than cetaceans to metabolize PCBs. The 2,3,7,8-tetrachlorodibenzo- p -dioxin equivalents of non- and mono- ortho PCBs in sea otters and certain prey species were at or above the theoretical threshold for toxic effects.

California↗
USGS2004

Influence of multiple water-quality characteristics on copper toxicity to fathead minnows (Pimephales promelas)

Water quality influences the bioavailability and toxicity of copper to aquatic organisms. Understanding the relationships between water-quality parameters and copper toxicity may facilitate the development of site-specific criteria for water quality and result in better protection of aquatic biota. Many studies have examined the influence of a single water-quality parameter on copper toxicity, but the interactions of several characteristics have not been well studied in low-hardness water. The goal of the present research was to examine the interactions among water-quality characteristics and their effects on copper toxicity to larval fathead minnows (Pimephales promelas). The effects of dissolved organic carbon (DOC) concentration, DOC source, pH, and hardness on acute copper toxicity were determined using a complete factorially designed experiment. Hardness, pH, DOC, and interaction of pH and DOC all significantly affected copper toxicity. A predictive model based on these data described 88% of the variability in copper toxicity. This model also explained 58% of the variability in copper toxicity for an independent dataset of South Carolina (USA) waters. The biotic ligand model underpredicted the acute copper toxicity to fathead minnows when compared with observed values.

Environmental Toxicology and Chemistry↗
USGS2005

Changes in productivity and contaminants in bald eagles nesting along the lower Columbia River, USA

Previous studies documented poor productivity of bald eagles (Haliaeetus leucocephalus) in the lower Columbia River (LCR), USA, and elevated p,p???-dichlorodiphenyldichloroethylene (DDE), polychlorinated biphenyls (PCBs), dioxins, and furans in eagle eggs. From 1994 to 1995, we collected partially incubated eggs at 19 of 43 occupied territories along the LCR and compared productivity and egg contaminants to values obtained in the mid-1980s. We found higher productivity at new nesting sites along the river, yet productivity at 23 older breeding territories remained low and was not different (p = 0.713) between studies. Eggshell thickness at older territories had not improved (p = 0.404), and eggshells averaged 11% thinner than shells measured before dichlorodiphenyltrichloroethane use. Decreases in DDE (p = 0.022) and total PCBs (p = 0.0004) in eggs from older breeding areas occurred between study periods. Productivity was not correlated to contaminants, but DDE, PCBs, and dioxin-like chemicals exceeded estimated no-effect values. Some dioxin-like contaminants in eggs were correlated to nest location, with highest concentrations occurring toward the river's mouth where productivity was lowest. Although total productivity increased due to the success of new nesting pairs in the region, egg contaminants remain high enough to impair reproduction at older territories and, over time, may alter productivity of new pairs nesting near the river's mouth. ?? 2005 SETAC.

Oregon, Washington↗
USGS2005

Exposure and effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin in tree swallows (Tachycineta bicolor) nesting along the Woonasquatucket River, Rhode Island, USA

Concentrations of 2,3,7,8-tetrachlorodibenzo- p -dioxin (TCDD) in tree swallows ( Tachycineta bicolor ) nesting along the Woonasquatucket River northwest of Providence (RI, USA) in 2000 and 2001 were some of the highest ever reported in avian tissues. Mean concentrations in eggs ranged from 300 to > 1,000 pg/g wet weight at the two most contaminated ponds, Allendale and Lyman. Mean egg concentrations at Greystone, the upstream reference pond, were 12 and 29 pg/g. Positive accumulation rates and concentrations in diet samples from 12-day-old nestlings indicated that the contamination was accumulated locally. Concentrations in diet of between 71 and 219 pg/g wet weight were more than 6 and 18 times higher than concentrations considered safe for birds (10–12 pg/g). Hatching success was negatively associated with concentration of TCDD in eggs. Only about half the eggs hatched at Allendale compared with >77% at Greystone. The national average for hatching success in successful nests is 85%. No other contaminants, such as polychlorinated biphenyls and mercury, were present in any sample at concentrations known to affect avian reproduction. Three bioindicators, half-peak coefficient of geometric variation, ethoxyresorufin- O -dealkylase activity, and brain asymmetry were assessed relative to TCDD contamination.

Rhode Island↗
USGS2005

Aroclor 1254 exposure reduces disease resistance and innate immune responses in fasted arctic charr

To examine the immunological impacts of polychlorinated biphenyls (PCBs) in an environmentally relevant way, we orally contaminated Arctic charr (Salvelinus alpinus) with Aroclor 1254. After contamination, fish were either fed (0 and 100 mg Aroclor 1254 kg-1 fish wt) or fasted (0, 1, 10, and 100 mg kg-1) to mimic cycles of feeding-fasting experienced by Arctic animals. After four months, PCB concentrations in muscle were the same in fasted and fed fish; however, PCBs in kidneys of fed fish were 33 to 50% of those in fasted fish. Arctic charr were exposed to Aeromonas salmonicida, the bacteria responsible for furunculosis, by cohabitation with infected conspecifics. Fasted fish had a significant trend toward lower survival with higher dose of PCBs - from 68% in controls to 48% in treatment involving 100 mg kg-1. Independent of PCB contamination, fed fish had the lowest survival; we attribute this to stress associated with establishing and maintaining feeding hierarchies. A significant decrease in the activity of lysozyme was observed in skin mucus, as was hemagglutination ability of a putative rhamnose lectin in fasted, but not in fed, PCB-treated fish. These results demonstrate the immunosuppressive effects of PCBs on Arctic charr, and they illustrate the importance of considering environmentally relevant nutritional status in ecotoxicological studies.

Environmental Toxicology and Chemistry↗
USGS2004

Susceptibility of the leaf-eating beetle, Galerucella calmariensis, a biological control agent for purple loosestrife (Lythrum salcaria), to three mosquito control larvicides

We evaluated the susceptibility of Galerucella calmariensis, a species used to control purple loosestrife (Lythrum salicaria), to three mosquito control larvicides. Larvae and adults were fed loosestrife cuttings dipped in Abate? (<375 g?L-1), Altosid? (<250 g?L-1), and Bacillus thuringiensis var israeliensis (Bti) (<110 g?L-1). Eggs on cuttings were dipped in the same concentrations. Pupae were immersed in Abate and Altosid solutions (<474.4 ug?L-1 and <1,169.2 ug?L-1, respectively). Hatching success of eggs dipped in Abate (>3.75 g?L-1) was reduced significantly and survival was significantly lower among larvae and adults eating cuttings dipped in Abate (>0.17 g?L-1 and >2.27 g?L-1, respectively). Hatching success of eggs dipped in Altosid (>2.52 g?L-1) was reduced significantly. With exposure to Altosid, larval survival to pupation and adult emergence was reduced significantly at concentrations of >2.92 g?L-1 and >0.63 g?L-1, respectively. Altosid (>0.23 g?L-1) also delayed the onset of pupation and adult emergence among larvae that survived to pupate. Larvae that survived with exposure to Altosid (>1.72 g?L-1) grew to 70% larger than those exposed to lower concentrations. Pupal survival was unaffected with exposure to Abate and Altosid and adult survival was unaffected with exposure to Altosid. Bacillus thuringiensis var israeliensis did not adversely affect any life stage of G. calmariensis. The mean Abate concentration on cuttings exposed to operational spraying was in the range that reduced egg hatchability and adult survival but was higher than concentrations that caused complete mortality of larvae. The mean Altosid concentration on cuttings exposed to operational spraying was in the range that reduced hatching success in eggs and delayed pupation and adult emergence of larvae.

Environmental Toxicology and Chemistry↗
USGS2005

Inhibition of microbial metabolism in anaerobic lagoons by selected sulfonamides, tetracyclines, lincomycin, and tylosin tartrate

Antibiotics are used to maintain healthy livestock and to promote weight gain in concentrated animal feed operations. Antibiotics rarely are metabolized completely by livestock and, thus, are often present in livestock waste and in waste-treatment lagoons. The introduction of antibiotics into anaerobic lagoons commonly used for swine waste treatment has the potential for negative impacts on lagoon performance, which relies on a consortium of microbes ranging from fermentative microorganisms to methanogens. To address this concern, the effects of eight common veterinary antibiotics on anaerobic activity were studied. Anaerobic microcosms, prepared from freshly collected lagoon slurries, were amended with individual antibiotics at 10 mg/L for the initial screening study and at 1, 5, and 25 mg/L for the dose-response study. Monitored metabolic indicators included hydrogen, methane, and volatile fatty acid concentrations as well as chemical oxygen demand. The selected antibiotics significantly inhibited methane production relative to unamended controls, thus indicating that antibiotics at concentrations commonly found in swine lagoons can negatively impact anaerobic metabolism. Additionally, historical antibiotic usage seems to be a potential factor in affecting methane production. Specifically, less inhibition of methane production was noted in samples taken from the lagoon with a history of multiple-antibiotic use.

Environmental Toxicology and Chemistry↗
USGS2005

Effects of contaminant exposure on reproductive success of ospreys (Pandion haliaetus) nesting in Delaware River and Bay, USA

Despite serious water-quality problems and pollutant loading and retention, Delaware River and Bay(USA) provide important wildlife habitat. In 2002, we conducted a comprehensive evaluation of contaminant exposure and reproduction of ospreys ( Pandion haliaetus ) breeding in Delaware River and Bay. Sample eggs were collected from 39 nests and analyzed for organochlorine pesticides, polychlorinated biphenyls (PCBs), and mercury; a subset of 15 eggs was analyzed for perfluorinated compounds and polybrominated diphenyl ethers (PBDEs). The fate of each nest was monitored weekly. Concentrations of 10 organochlorine pesticides or metabolites, total PCBs, and several toxic PCB congeners were greater ( p < 0.05) in eggs collected between the Chesapeake and Delaware Canal (C and D Canal) and Trenton (Delaware River and northern Bay) compared to other sites. Concentrations of p,p ′-dichlorodiphenyldichloroethylene ( p,p ′-DDE; 0.785–3.84 μg/g wet wt) and total PCBs (5.50–14.5 μg/g wet wt) in eggs collected between the C and D Canal and Trenton were similar to levels recently found in the Chesapeake Bay. In all study segments, at least one young fledged from 66 to 75% of nests. Productivity for Delaware Inland Bays (reference area) and southern Delaware Bay was 1.17 and 1.42 fledglings/active nest, respectively; north of the C and D Canal, productivity was 1.00 fledgling/active nest, which is marginally adequate to maintain the population. Using these data, a logistic regression model found that contaminant concentrations ( p,p ′-DDE, heptachlor epoxide, chlordane and metabolites, and total PCBs) were predictive of hatching success. Several perfluorinated compounds and PBDEs were detected in eggs at concentrations approaching 1 μg/g wet weight. These findings provide evidence that contaminants continue to be a significant stressor on osprey productivity in the northern Delaware River and Bay.

Delaware, New Jersey, Pennsylvania,↗
USGS2005

Novel biomarkers of perchlorate exposure in zebrafish

Perchlorate inhibits iodide uptake by thyroid follicles and lowers thyroid hormone production. Although several effects of perchlorate on the thyroid system have been reported, the utility of these pathologies as markers of environmental perchlorate exposures has not been adequately assessed. The present study examined time-course and concentration-dependent effects of perchlorate on thyroid follicle hypertrophy, colloid depletion, and angiogenesis; alterations in whole-body thyroxine (T4) levels; and somatic growth and condition factor of subadult and adult zebrafish. Changes in the intensity of the colloidal T4 ring previously observed in zebrafish also were examined immunohistochemically. Three-month-old zebrafish were exposed to ammonium perchlorate at measured perchlorate concentrations of 0, 11, 90, 1,131, and 11,480 ppb for 12 weeks and allowed to recover in clean water for 12 weeks. At two weeks of exposure, the lowest-observed-effective concentrations (LOECs) of perchlorate that induced angiogenesis and depressed the intensity of colloidal T4 ring were 90 and 1,131 ppb, respectively; other parameters were not affected (whole-body T4 was not determined at this time). At 12 weeks of exposure, LOECs for colloid depletion, hypertrophy, angiogenesis, and colloidal T4 ring were 11,480, 1,131, 90, and 11 ppb, respectively. All changes were reversible, but residual effects on angiogenesis and colloidal T4 ring intensity were still present after 12 weeks of recovery (LOEC, 11,480 ppb). Whole-body T 4 concentration, body growth (length and weight), and condition factor were not affected by perchlorate. The sensitivity and longevity of changes in colloidal T4 ring intensity and angiogenesis suggest their usefulness as novel markers of perchlorate exposure. The 12-week LOEC for colloidal T4 ring is the lowest reported for any perchlorate biomarker in aquatic vertebrates. ?? 2005 SETAC.

Environmental Toxicology and Chemistry↗
USGS2005

Widespread detection of N, N-diethyl-m-toluamide in U.S. streams: Comparison with concentrations of pesticides, personal care products, and other organic wastewater compounds

One of the most frequently detected organic chemicals in a nationwide study concerning the effects of wastewater on stream water quality conducted in the year 2000 was the widely used insect repellant N , N -diethyl- m -toluamide (DEET). It was detected at levels of 0.02 &mu;g/L or greater in 73% of the stream sites sampled, with the selection of sampling sites being biased toward streams thought to be subject to wastewater contamination (i.e., downstream from intense urbanization and livestock production). Although DEET frequently was detected at all sites, the median concentration was low (0.05 &mu;g/L). The highest concentrations of DEET were found in streams from the urban areas (maximum concentration, 1.1 &mu;g/L). The results of the present study suggest that the movement of DEET to streams through wastewater-treatment systems is an important mechanism that might lead to the exposure of aquatic organisms to this chemical.

Environmental Toxicology and Chemistry↗