Broad-host-range plasmids in treated wastewater effluent and receiving streams

The occurrence of broad-host-range (BHR) plasmid amplicons belonging to incompatibility (Inc) groups IncA/C, IncN, IncP, and IncW in two wastewater treatment plant (WWTP) effluents and effluent-receiving streams in Northwest Arkansas, Mud Creek and Spring Creek, was determined. Community DNA captured on filter membranes and plasmid DNA extracted from antibiotic-resistant Escherichia coli isolated from Mud Creek was used for polymerase chain reaction at amplification of partial gene sequences specific to BHR plasmids. IncP plasmid amplicons were detected in effluent and downstream sites in both streams, while IncN and IncW plasmid amplicons were detected in Spring Creek in effluent and downstream but not upstream. IncA/C plasmid amplicons, in contrast, were detected at all sites, including upstream in most samples in Spring Creek and in one sample from Mud Creek. One IncP and two IncN were the only BHR plasmid amplicons found in 85 screened antibiotic-resistant E. coli isolates, and were detected only in isolates from effluent and downstream samples. Broad-host-range plasmids frequently carry antibiotic-resistance genes and can facilitate horizontal transfer of those genes. While BHR plasmids have been detected in WWTPs, WWTPs do not target these genetic elements for destruction. This study indicates that BHR plasmids are in WWTP effluent and are introducing BHR plasmids into streams. Additionally, species other than E. coli may be better targets as indicator bacteria for future studies of the impact of treated effluent on environmental dissemination of BHR plasmids.     

Wastewater Effluent,Combined Sewer Overflows,and Other Sources of Organic Compounds to Lake Champlain1

Abstract: Some sources of organic wastewater compounds (OWCs) to streams, lakes, and estuaries, including wastewater‐treatment‐plant effluent, have been well documented, but other sources, particularly wet‐weather discharges from combined‐sewer‐overflow (CSO) and urban runoff, may also be major sources of OWCs. Samples of wastewater‐treatment‐plant (WWTP) effluent, CSO effluent, urban streams, large rivers, a reference (undeveloped) stream, and Lake Champlain were collected from March to August 2006. The highest concentrations of many OWCs associated with wastewater were in WWTP‐effluent samples, but high concentrations of some OWCs in samples of CSO effluent and storm runoff from urban streams subject to leaky sewer pipes or CSOs were also detected. Total concentrations and numbers of compounds detected differed substantially among sampling sites. The highest total OWC concentrations (10‐100 μg/l) were in samples of WWTP and CSO effluent. Total OWC concentrations in samples from urban streams ranged from 0.1 to 10 μg/l, and urban stream‐stormflow samples had higher concentrations than baseflow samples because of contributions of OWCs from CSOs and leaking sewer pipes. The relations between OWC concentrations in WWTP‐effluent and those in CSO effluent and urban streams varied with the degree to which the compound is removed through normal wastewater treatment. Concentrations of compounds that are highly removed during normal wastewater treatment [including caffeine, Tris(2‐butoxyethyl)phosphate, and cholesterol] were generally similar to or higher in CSO effluent than in WWTP effluent (and ranged from around 1 to over 10 μg/l) because CSO effluent is untreated, and were higher in urban‐stream stormflow samples than in baseflow samples as a result of CSO discharge and leakage from near‐surface sources during storms. Concentrations of compounds that are poorly removed during treatment, by contrast, are higher in WWTP effluent than in CSO, due to dilution. Results indicate that CSO effluent and urban stormwaters can be a significant major source of OWCs entering large water bodies such as Burlington Bay.     

Lagrangian Sampling for Emerging Contaminants Through an Urban Stream Corridor in Colorado1

Abstract: Recent national concerns regarding the environmental occurrence of emerging contaminants (ECs) have catalyzed a series of recent studies. Many ECs are released into the environment through discharges from wastewater treatment plants (WWTPs) and other sources. In 2005, the U.S. Geological Survey and the City of Longmont initiated an investigation of selected ECs in a 13.8‐km reach of St. Vrain Creek, Colorado. Seven sites were sampled for ECs following a Lagrangian design; sites were located upstream, downstream, and in the outfall of the Longmont WWTP, and at the mouths of two tributaries, Left Hand Creek and Boulder Creek (which is influenced by multiple WWTP outfalls). Samples for 61 ECs in 16 chemical use categories were analyzed and 36 were detected in one or more samples. Of these, 16 have known or suspected endocrine‐disrupting potential. At and downstream from the WWTP outfall, detergent metabolites, fire retardants, and steroids were detected at the highest concentrations, which commonly exceeded 1 μg/l in 2005 and 2 μg/l in 2006. Most individual ECs were measured at concentrations less than 2 μg/l. The results indicate that outfalls from WWTPs are the largest but may not be the sole source of ECs in St. Vrain Creek. In 2005, high discharge was associated with fewer EC detections, lower total EC concentrations, and smaller EC loads in St. Vrain Creek and its tributaries as compared with 2006. EC behavior differed by individual compound, and some differences between sites could be attributed to analytical variability or to other factors such as physical or chemical characteristics or distance from contributing sources. Loads of some ECs, such as diethoxynonylphenol, accumulated or attenuated depending on location, discharge, and distance downstream from the WWTP, whereas others, such as bisphenol A, were largely conservative. The extent to which ECs in St. Vrain Creek affect native fish species and macroinvertebrate communities is unknown, but recent studies have shown that fish respond to very low concentrations of ECs, and further study on the fate and transport of these contaminants in the aquatic environment is warranted.     

Chemical and toxicologic assessment of organic contaminants in surface water using passive samplers

Passive sampling methodologies were used to conduct a chemical and toxicologic assessment of organic contaminants in the surface waters of three geographically distinct agricultural watersheds. A selection of current-use agrochemicals and persistent organic pollutants, including polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and organochlorine pesticides, were targeted using the polar organic chemical integrative sampler (POCIS) and the semipermeable membrane device passive samplers. In addition to the chemical analysis, the Microtox assay for acute toxicity and the yeast estrogen screen (YES) were conducted as potential assessment tools in combination with the passive samplers. During the spring of 2004, the passive samplers were deployed for 29 to 65 d at Leary Weber Ditch, IN; Morgan Creek, MD; and DR2 Drain, WA. Chemical analysis of the sampler extracts identified the agrochemicals predominantly used in those areas, including atrazine, simazine, acetochlor, and metolachlor. Other chemicals identified included deethylatrazine and deisopropylatrazine, trifluralin, fluoranthene, pyrene, cis- and trans-nonachlor, and pentachloroanisole. Screening using Microtox resulted in no acutely toxic samples. POCIS samples screened by the YES assay failed to elicit a positive estrogenic response.     

CAGED FISH AS MONITORS OF POLLUTION: EFFECTS OF CHLORINATED EFFLUENT FROM A WASTEWATER TREATMENT PLANT1

ABSTRACT: Fish confined to cages were used to determine the effects of effluent from a wastewater treatment plant (WWTP). Control fish were kept in cages in an aquaculture pond. Acute effects of the effluent entering the final oxidation pond of the WWTP were determined by confining channel catfish (Ictalurus punctatus) at the pond inlet; the mean total residual chlorine (TRC) concentration was 0.9 mg/l during this exposure. After 8 h, 42 percent of the fish had died and survivors had severe lesions of the skin and gills. During the first two weeks of exposure, channel catfish at the outlet of the final oxidation pond (mean TRC=0.1 mg/l) were predisposed to bacterial infection but lost the parasitic trematodes that were on the gills when the fish were placed in cages. After several weeks, exposed fish had histologic lesions, enlarged livers, and reduced growth. The presence of unidentified carcinogen(s) in the effluent of this WWTP was indicated by papillomas developing on caged black bullheads (Ictalurus melas) and hepatic-enzyme induction in channel catfish. In situ exposure of caged fish was advantageous because storage and pretreatment of water samples were not required, and exposure levels corresponded to those present in the environment. The use of cages for containment of fish during field exposure allowed confinement to the location of interest and convenient sampling of the fish. Unlike wild fish, the caged fish could be compared to control fish with the same pre-exposure history.     

Transport and metabolic fate of sewage particles in a recipient stream

Although the implementation of wastewater treatment plants (WWTP) has dramatically increased the quality of surface waters in urbanized areas, WWTPs can still discharge noticeable amounts of solutes and particles to recipient streams. Although the fate of WWTP nutrients has received considerable attention, transport and in-stream transformation of sewage-derived particulate organic matter (SDPOM) have not. To investigate the transport and transformation of SDPOM in recipient streams, we experimentally injected fluorescently labeled SDPOM into a headwater stream and tracked its downstream fate at baseflow. Most SDPOM disappeared from the streamwater within a 160-m long reach with an average deposition velocity of 0.14 mm s(-1). We further coupled hydrometric measurements of specific water fluxes through the streambed interface with a mixing model to estimate streambed oxygen removal, and found significantly higher oxygen removal in the deposition (0.75 g O2 m(-2) d(-1)) than in the downstream post-deposition (0.36 g O2 m(-2) d(-1)) subreach. Contrary to our expectations, we did not detect any apparent effect of SDPOM deposition on streambed clogging. Our results show the capacity of a recipient stream to retain SDPOM and to reduce its downstream export, and thus contribute to a better understanding of ecosystem services of human-altered streams.     

Investigating the quantitative and qualitative status of effluent in the wastewater treatment plant in Iran Central Iron Ore

The aim of present study was to investigate the quality of the produced effluent from different units of the Iran Central Iron Ore in Bafq city and comparison of effluent with the standards. This study presents the physicochemical and biological parameters data of effluent of three Sequencing batch reactors (SBR) with a capacity of 160 m³?d^?1. Most common parameters include pH, total suspended solids (TSS), total nitrogen (TN), total phosphorus (TP), biochemical oxygen demand (BOD₅), chemical oxygen demand (COD), heavy metals, and total coliforms and fecal coliforms as biological indicators. Then, for each SBR system, the average of each parameter was determined, and results were compared with the standard recommended by the Iranian Environmental Protection Agency. Based on the results, some of the parameters, including BOD₅, COD, and TSS in the wastewater treatment plant (WWTP) effluent, are higher than the permitted amount for discharge to the surface water. Considering the BOD₅, COD, and TSS concentration in WWTPs, the treated wastewater is only suitable for agricultural and irrigation use. Therefore, wastewater produced by Iran Central Iron Ore Co. will need additional treatment to achieve standard quality of water before discharge in surface water and adsorbent well.     

On‐Site Exposure to Treated Wastewater Effluent Has Subtle Effects on Male Fathead Minnows and Pronounced Effects on Carp

This study tested the hypotheses that (1) exposure to treated Water Reclamation Plant (WRP) effluent will induce biological effects in exposed fish that are consistent with environmental estrogen (EE) exposure; and (2) seasonal differences in effluent composition will moderate biological effects. We conducted seven on‐site exposures using a mobile laboratory. Total estrogenicity of effluents was 10‐ to 20‐fold higher during spring than in fall. Common EEs including steroid estrogens, alkylphenols, and bisphenol‐A were ubiquitous. An unusual spike in total estrogenicity identified a combined sewer overflow event. Fathead minnows (Pimephales promelas) responded to exposure with subtle changes in vitellogenin concentrations and secondary sex characteristics. An opportunity to assess a common carp (Cyprinus carpio) population permanently sustained inside the Stickney WRP revealed pronounced exposure effects, but also the resilience of biological organisms even under long‐term exposure. In contrast to other studies, no histopathological changes were found. The mobile exposure laboratory proved capable of maintaining U.S. Environmental Protection Agency‐recommended exposure conditions while providing flexibility for rapid deployment at multiple sites with minimal operational disruption. Further studies using this platform hold promise to resolve the convoluted interactions between complex effluents and inherent biological complexity.     

Contribution of Wastewater Treatment Plant Effluents to Nutrient Dynamics in Aquatic Systems: A Review

Excessive nutrient loading (considering nitrogen and phosphorus) is a major ongoing threat to water quality and here we review the impact of nutrient discharges from wastewater treatment plants (WWTPs) to United States (U.S.) freshwater systems. While urban and agricultural land uses are significant nonpoint nutrient contributors, effluent from point sources such as WWTPs can overwhelm receiving waters, effectively dominating hydrological characteristics and regulating instream nutrient processes. Population growth, increased wastewater volumes, and sustainability of critical water resources have all been key factors influencing the extent of wastewater treatment. Reducing nutrient concentrations in wastewater is an important aspect of water quality management because excessive nutrient concentrations often prevent water bodies from meeting designated uses. WWTPs employ numerous physical, chemical, and biological methods to improve effluent water quality but nutrient removal requires advanced treatment and infrastructure that may be economically prohibitive. Therefore, effluent nutrient concentrations vary depending on the particular processes used to treat influent wastewater. Increasingly stringent regulations regarding nutrient concentrations in discharged effluent, along with greater freshwater demand in populous areas, have led to the development of extensive water recycling programs within many U.S. regions. Reuse programs provide an opportunity to reduce or eliminate direct nutrient discharges to receiving waters while allowing for the beneficial use of reclaimed water. However, nutrients in reclaimed water can still be a concern for reuse applications, such as agricultural and landscape irrigation.     

Nutrient Uptake in a Large Urban River1

Abstract: Small streams have been shown to be efficient in retaining nutrients and regulating downstream nutrient fluxes, but less is known about nutrient retention in larger rivers. We quantified nutrient uptake length and uptake velocity in a regulated urban river to determine the river’s ability to retain nutrients associated with wastewater treatment plant (WWTP) effluent. We measured net uptake of soluble reactive phosphorus (SRP), dissolved organic phosphorus, ammonium (NH₄), nitrate, and dissolved organic nitrogen in the Chattahoochee River, Atlanta, GA by following the downstream decline of nutrients and fluoride from WWTP effluent on 10 dates under low flow conditions. Uptake of all nutrients was sporadic. On many dates, there was no evidence of measurable nutrient uptake lengths within the reach; indeed, on several dates release of inorganic N and P within the sample reach led to increased nutrient export downstream. When uptake occurred, SRP uptake length was negatively correlated with total suspended solids and temperature. Uptake velocities of SRP and NH₄ in the Chattahoochee River were lower than velocities in less‐modified systems, but they were similar to those measured in other WWTP impacted systems. Lower uptake velocities indicate a diminished capacity for nutrient uptake.     

Pharmaceuticals and other organic chemicals in selected north-central and northwestern Arkansas streams

Recently, our attention has focused on the low level detection of many antibiotics, pharmaceuticals, and other organic chemicals in water resources. The limited studies available suggest that urban or rural streams receiving wastewater effluent are more susceptible to contamination. The purpose of this study was to evaluate the occurrence of antibiotics, pharmaceuticals, and other organic chemicals at 18 sites on seven selected streams in Arkansas, USA, during March, April, and August 2004. Water samples were collected upstream and downstream from the influence of effluent discharges in northwestern Arkansas and at one site on a relatively undeveloped stream in north-central Arkansas. At least one antibiotic, pharmaceutical, or other organic chemical was detected at all sites, except at Spavinaw Creek near Mayesville, Arkansas. The greatest number of detections was observed at Mud Creek downstream from an effluent discharge, including 31 pharmaceuticals and other organic chemicals. The detection of these chemicals occurred in higher frequency at sites downstream from effluent discharges compared to those sites upstream from effluent discharges; total chemical concentration was also greater downstream. Wastewater effluent discharge increased the concentrations of detergent metabolites, fire retardants, fragrances and flavors, and steroids in these streams. Antibiotics and associated degradation products were only found at two streams downstream from effluent discharges. Overall, 42 of the 108 chemicals targeted in this study were found in water samples from at least one site, and the most frequently detected organic chemicals included caffeine, phenol, para-cresol, and acetyl hexamethyl tetrahydro naphthalene (AHTN).     

A river water quality model integrated with a web-based geographic information system

Scientists often use mathematical models to assess river water quality. However, the application of the models in environmental management and risk assessment is quite limited because of the difficulty of preparing input data and interpreting model output. This paper presents a study that links ArcIMS, a Web-based Geographic Information System (GIS) software to ROUT, a national and regional scale river model which evolved from the US Environmental Protection Agency's Water Use Improvement and Impairment Model, to create a WWW-GIS-based river simulation model called GIS-ROUT. GIS-ROUT is used to predict chemical concentrations in perennially flowing rivers throughout the continental United States that receive discharges from more than 10,000 publicly owned wastewater treatment plants (WWTPs). The WWTP chemical loadings are calculated from per capita per day disposal of product ingredients and the population served by each plant. Each WWTP, containing data on treatment type and influent and effluent flows, is spatially associated with a specific receiving river segment. Based on user defined treatment-type removal rates for a particular chemical, an effluent concentration for each WWTP is calculated and used as input to the river model. Over 360,000 km of rivers are modeled, incorporating dilution and first order loss of the chemical in each river segment. The integration of spatial data, GIS, the WWW, and modeling in GIS-ROUT makes it possible to organize and analyze data spatially, and view results on interactive maps as well as tables and distribution charts. The integration allows scientists and managers in different locations to coordinate and share their estimations for environmental exposure and risk assessments.     

Sorption, mobility, and transformation of estrogenic hormones in natural soil

Potent estrogenic hormones are consistently detected in the environment at low concentration, yet these chemicals are strongly sorbed to soil and are labile. The objective of this research was to improve the understanding of the processes of sorption, mobility, and transformation for estrogens in natural soils, and their interaction. Equilibrium and kinetic batch sorption experiments, and a long-term column study were used to study the fate and transport of 17beta-estradiol and its primary metabolite, estrone, in natural soil. Kinetic and equilibrium batch experiments were done using radiolabeled 17beta-estradiol and estrone. At the concentrations used, it appeared that equilibrium sorption for both estrogens was achieved between 5 and 24 h, and that the equilibrium sorption isotherms were linear. The log K(oc) values for 17beta-estradiol (2.94) and estrone (2.99) were consistent with previously reported values. Additionally, it was found that there was rate-limited sorption for both 17beta-estradiol (0.178 h(-1)) and estrone (0.210 h(-1)). An approximately 42 h long, steady-flow, saturated column experiment was used to study the transport of radiolabeled 17beta-estradiol, which was applied in a 5.00 mg L(-1) solution pulse for 44 pore volumes. 17beta-estradiol and estrone were the predominant compounds detected in the effluent. The effluent breakthrough curves were asymmetric and the transport modeling indicated that sorption was rate-limited. Sorption rates and distributions of the estrogens were in agreement between column and batch experiments. This research can provide a better link between the laboratory results and observations in the natural environment.     

Assessment of Endocrine‐Disrupting Chemicals Attenuation in a Coastal Plain Stream Prior to Wastewater Treatment Plant Closure

The U.S. Geological Survey is conducting a combined pre/post‐closure assessment at a long‐term wastewater treatment plant (WWTP) site at Fort Gordon near Augusta, Georgia. Here, we assess select endocrine‐active chemicals and benthic macroinvertebrate community structure prior to closure of the WWTP. Substantial downstream transport and limited instream attenuation of endocrine‐disrupting chemicals (EDCs) was observed in Spirit Creek over a 2.2‐km stream segment downstream of the WWTP outfall. A modest decline (less than 20% in all cases) in surface water detections was observed with increasing distance downstream of the WWTP and attributed to partitioning to the sediment. Estrogens detected in surface water in this study included estrone (E1), 17β‐estradiol (E2), and estriol (E3). The 5 ng/l and higher mean estrogen concentrations observed in downstream locations indicated that the potential for endocrine disruption was substantial. Concentrations of alkylphenol ethoxylate (APE) metabolite EDCs also remained statistically elevated above levels observed at the upstream control site. Wastewater‐derived pharmaceutical and APE metabolites were detected in the outflow of Spirit Lake, indicating the potential for EDC transport to aquatic ecosystems downstream of Fort Gordon. The results indicate substantial EDC occurrence, downstream transport, and persistence under continuous supply conditions and provide a baseline for a rare evaluation of ecosystem response to WWTP closure.     

Estrogenic activity in the environment: municipal wastewater effluent, river, ponds, and wetlands

Estrogenic activity of regional water samples was evaluated. Samples obtained from wetlands and ponds involved in various agricultural land uses, from three river sites over four seasons, and from municipal wastewater effluent held in storage lagoons were evaluated. The estrogen-responsive cell line MCF-7 BOS was used in the E-screen assay to determine 17beta-estradiol equivalents (E2 Eq) of water samples extracted by solid-phase extraction. Estrogenic activity in surrounding wetlands and ponds from different land uses was not different, with 10(-12) M E2 Eq (0.3 ppt). Estrogenic activity of Red River samples was within the same range as wetland-pond samples. The highest activity was found downstream from municipal wastewater treatment effluent discharge sites, in winter when river flow was lowest (approximately 6 x 10(-13) M E2 Eq). Results showed that 7 of 20 wetland-pond samples and 5 of 12 river samples were below the limits of quantitation (approximately 3 x 10(-14) M E2 Eq). Toxicity was found in fall and summer river samples upstream from municipal wastewater release sites. The timing of toxicity did not coincide to the presence of elevated fecal coliforms. Estrogenic activity in wastewater effluent from lagoons decreased over time (approximately 25 to 5 x 10(-13) M E2 Eq) with an apparent half-life of 8 d for one lagoon. The median concentration of detectable estrogenic activity in regional water samples was approximately 50-fold less than the median 17beta-estradiol concentration of estradiol detected in some U.S. streams in previous studies.     

EFFECTS OF NO-FLOW RIVER CONDITIONS ON THE PLATTE RIVER WELL FIELD1

ABSTRACT: Effects of no-flow river conditions on the quantity and quality of water in the Platte River well field of the City of Grand Island, Nebraska, were examined utilizing a finite-difference computer simulation model specifically developed for this well field. Results suggest that the effects of these no-flow periods on water quality may be most important. In particular, the no-flow periods eliminate the hydraulic barrier between the well field and an area north of the River that is contaminated with nitrate (concentrations in the 20 to 40 mg/1 NO₃-N range). They also change the direction and velocity of movement of the contaminated ground water. Simulation results indicate that contaminated ground water moves toward the well field with a velocity of 0.42 ft/d after 30 days of no-flow and 1.43 ft/d after 180 days of no-flow. Limiting no-flow conditions to 10 consecutive days would protect the well field.     

ASSESSMENT OF HYDRAULIC PROPERTIES IN AN UNCONFINED ALLUVIAL AQUIFER NEAR GRAND ISLAND,NEBRASKA1

ABSTRACT: A method is presented to analyze time-drawdown data from one or more observation wells for the calculation of four hydraulic parameters for unconfined aquifers: vertical hydraulic conductivity, horizontal hydraulic conductivity, storage coefficient, and specific yield. The hydraulic parameter results are further analyzed for reliability and the possible ranges of the actual parameter values. After verification using a theoretical example, the method was used to analyze pumping test data from 22 observation wells in an unconfined alluvial aquifer near Grand Island, Nebraska. Results indicate that this method can be used to efficiently calculate the four hydraulic parameters in this type of aquifer. The method can also identify the impact of measurement errors on the parameter estimates, and provide ranges of the actual parameter values. The parameter values calculated using this method were compared to those determined using other theories. It is found that this method is very useful for calculating the hydraulic properties from pumping test data and for analyzing the parameter reliability.     

SITING OF A WATER POLLUTION CONTROL FACILITY AT JAMESTOWN,RHODE ISLAND1

ABSTRACT: The town of Jamestown, Rhode Island, located on Conanicut Island in Narragansett Bay, is constructing a secondary treatment plant in order to comply with NPDES regulations. Twelve candidate sites for the plant and marine outfall were initially proposed, and ability to meet State water quality standards at these sites was evaluated using an EPA buoyant plume model. A final outfall site, Taylor Point, was selected by the Town from among the sites considered acceptable. Taylor Point was then subjected to field hydrographic studies including drogue tracking, current recordings, and tracer dye surveys. Results of the measurement program served as input to a two-dimensional effluent dispersion model which predicted excess BOD, coliform, and suspended solids resulting from effluent discharge off Taylor Point. The model predictions demonstrated that State water quality standards can be maintained outside the initial discharge plume.     

The Effect of Estrogens,River Water,and Treated Wastewater on Vitellogenin Induction of Japanese Medaka1

Abstract: The objective of this study is to evaluate the effect of estrogens on fish endocrine disruption in river water and treated wastewater. Endogenous estrogen estrone (E1), 17β‐estradiol (E2), river water, and treated wastewater were used for exposure tests on male Japanese medaka. Vitellogenin induction in male medaka was regarded as the endpoint of endocrine disruption. The effective concentrations of E1 and E2 on vitellogenin induction in medaka were evaluated by breeding medaka for 14 days in tanks with various concentrations of E1 or E2. Vitellogenin induction increased with elapse of time during exposure, with higher estrogen concentrations causing greater vitellogenin induction. According to the test results, the lowest observed effect concentrations (LOECs) of E1 and E2 were estimated to be 31.6 and 5.0 ng/l, respectively; and the E2 equivalent (EEQ) LOEC value of E1 was 5.2 ng‐E2/l, derived by multiplying the relative potency of E1 by that of E2 as estimated in this study. In continuous exposure tests using river water or treated wastewater, the estrogenic activity, an index of total estrogenic potential measured by yeast screen assay and expressed as EEQ, varied widely during the exposure tests, and significant vitellogenin induction was observed after several days of high levels of estrogenic activity in water. Vitellogenin concentration tended to significantly increase if EEQ exceeded the level of 5 ng‐E2/l. The threshold value was substantially the same as the results for E1 and E2 exposure tests of medaka. Consequently, EEQ over 5 ng‐E2/l was revealed to have the potential to cause endocrine disruption of male medaka. As estrogenic activity exceeding 5 ng‐E2/l was observed in some rivers in Japan, total estrogenic potential needs to be further decreased at wastewater treatment plants to prevent fish endocrine disruption.     

Fathead Minnow and Bluegill Sunfish Life‐Stage Responses to 17β‐Estradiol Exposure in Outdoor Mesocosms

Developmental and reproductive effects of 17β‐estradiol (E2) exposure on two generations of fathead minnows and one generation of bluegill sunfish were assessed. Fish were exposed to E2 for six continuous weeks in outdoor mesocosms simulating natural lake environments. First generation fish were exposed while sexually mature. Second generation fathead minnows were exposed either during early development, sexual maturity, or both stages. Multiple endpoints were measured to assess effects of E2 exposure on fecundity and fish health and development. Plasma vitellogenin concentrations were highly variable in all fish. Differences in egg production timing for both species indicate differences in fecundity between females exposed to E2 and controls. First generation fathead minnows exposed to E2 had lower body condition factors and reduced secondary sexual characteristic expression by males. Only a difference in relative liver weight was observed in second generation fathead minnows. First generation bluegill males exposed to E2 had significantly smaller testes compared to controls. Although fish response was highly variable, results indicate that exposure to E2 at environmentally relevant concentrations affect fathead minnow and bluegill sunfish health and development, which may have implications for the health and sustainability of fish populations. Furthermore, exposure timing and environmental factors affect fish response to E2 exposure.