Impacts of Fulvic Acid on the Toxicity of the Herbicide Atrazine to Lemna minor.

Fulvic acids (FA) are environmentally prevalent components of dissolved organic carbon. Little research has evaluated their potential influence on the bioavailability of herbicides to non-target aquatic plants. This study evaluated the potential impacts of FA on the bioavailability of atrazine (ATZ) to the aquatic plant Lemna minor. Plants were exposed to 0, 15, 30, 60, 125, and 750 µg/L ATZ in media containing three FA concentrations (0, 5, and 15 mg/L) in a factorial study under static conditions. Fronds were counted after 7- and 14-days exposure and intrinsic growth rates (IGR) and total frond yields were calculated for analysis. Atrazine NOAECs and LOAECs within each FA treatment series (0, 5, or 15 mg/L) were identified and EC50s were estimated. NOAEC/LOAECs for yield and IGR were 60/125 µg/L except for yield in the 0 mg/L-FA series (30/60) and IGR in the 5 mg/L-FA series (30/60). NOAEC/LOAECs were 30/60 µg/L for all treatments and both endpoints after 14 days exposure. EC50s ranged from 88.2 to 106.1 µg/L (frond production 7 DAT), 158.0-186.0 µg/L (IGR, 7 DAT), 74.7-86.3 µg/L (frond production, 14 DAT), and 144.1-151.3 µg/L (IGR, 14 DAT). FA concentrations did not influence the toxicity of ATZ.

Absorption, translocation, and metabolism of atrazine, carbamazepine, and sulfamethoxazole by the macrophyte Orange King Humbert canna lily (Canna × generalis L.H. Bailey (pro sp.) [glauca × indica]).

Canna × generalis L.H. Bailey (pro sp.) [glauca × indica] (common name: Orange King Humbert canna lily) has been reported as a promising plant species that can effectively remove contaminants of emerging concern (CECs), such as atrazine (ATZ), carbamazepine (CBZ), and sulfamethoxazole (SMX), from contaminated surface water. In the present study, absorption, translocation, and metabolism of such CECs in canna were examined using carbon-14-labeled ([14C]) analogues of each contaminant to understand the removal of each. Uptake/adsorption of the [14C]-CECs increased over time and was > 47.5% at the end of the 14-day study. The root-shoot translocation of [14C]-ATZ in canna was the greatest at 49.9-78.8%, followed by [14C]-CBZ (1.9-44.7%) and [14C]-SMX (3.3-6.0%). The cumulative transpiration of canna was correlated with absorption (R2 > 0.95) and root-shoot translocation (R2 > 0.97) magnitudes of [14C]-CECs in canna. Radiographic results revealed significant conversion of parent [14C]-CECs into other metabolites during the 14-day study. Metabolism of [14C]-ATZ and [14C]-CBZ occurred mainly in the shoots, whereas metabolism of [14C]-SMX occurred in the roots. Taken together, root-shoot redistribution and metabolism of CECs absorbed into canna can vary by transpiration volume as well as chemical properties.

Influence of Sediments on Concentrations of Fluridone and Penoxsulam in the Water Column and Sediment Pore Water.

Control of invasive aquatic plants is crucial for the maintenance of chemical, biological and ecological balances in many fresh water systems. Exposure of invasive plants to herbicides used for their control may be reduced by sorption to organic matter in sediments. Since granular herbicide formulations have closer contact with sediments (compared to liquid formulations), concentrations in the water column may be much lower. To test this hypothesis, microcosms containing sediments with < 1%, 6.4%, 19.7%, and 44% organic matter were treated with liquid and granular formulations of fluridone and penoxsulam. Herbicide concentrations in the water column and sediment pore water were monitored over 40 days. The presence of sediments (regardless of organic carbon content) significantly reduced concentrations of fluridone in the water column from the granular formulations relative to the liquid formulation. A similar, though less extreme, pattern was observed for penoxsulam in most of the organic carbon treatments.

Influence of Water Resource Recovery Facility Effluents on the Presence of Selected Trace Organic Contaminants (TOrCs) in the Reedy River, South Carolina.

Wastewater reclamation facilities are known sources of emerging contaminants associated with human health and sanitation. This study evaluated the contribution of trace organic contaminants to a previously unmonitored river by water resource reclamation facilities. Six sampling events were conducted on the Reedy River in South Carolina. Sampling locations included sites upstream and downstream of two WRRFs located on the river to examine potential contributions under drought conditions where WRRF effluents comprise a large proportion of total stream flow. Five target analytes were monitored including atrazine, carbamazepine, 17ß-estradiol, perfluorooctanoic acid, and sulfamethoxazole. On a mass basis, the WRRFs contributed additional loadings of carbamazepine ranging from 5.4 g/d to 7.2 g/d (mean: 6.3 ± 0.4 g/d), PFOA ranging from 8.6 to 31.9 g/d (mean: 20.0 ± 4.9), and sulfamethoxazole ranging from 49.4 g/d to 75.1 g/d (mean: 62.1 ± 4.8). 17ß-estradiol was detected once and atrazine was not detected.

Losses of selected pesticides in drainage water from containerized ornamental plants.

Limited research has focused on factors affecting pesticide losses from ornamental plant production nurseries. This project evaluated the effects of overhead irrigation or simulated rainfall intensity and formulation and application methods on the losses of acephate, bifenthrin, and imidacloprid in drainage water. The liquid formulation of each respective pesticide was applied to individual replicates (potted Ilex cornuta Lindl. & Paxton plant on a drainage collection saucer) as substrate-applied drenches or foliar sprays (acephate and bifenthrin only). Granular formulations of acephate and imidacloprid were spread across the tops of media in pots. After application of treatments, irrigation or simulated rainfall was applied daily for 19 consecutive days at rates of 42.3 ± 4.57, 56.7 ± 7.92, and 95.4 ± 19.47 ml min-1 , and drainage water from individual replicates was collected for analysis. Irrigation or simulated rainfall intensity had no effects on losses of the pesticides under the conditions tested. Concentrations in drainage of all three pesticides were highest from the drench applications, whereas respective foliar spray applications resulted in the lowest active ingredient concentrations in drainage. The percentage of active ingredient lost in drainage water ranged from a minimum of 0.2 ± 0.05% (mean ± SE) for granular acephate to a maximum of 19.5 ± 3.14% (mean ± SE) for the imidacloprid drench. Most pesticide losses occurred within the first 2 d after application of drenches or sprays. Granular formulations had a longer period of release, indicating a risk of loss from overirrigation during an extended period. Results emphasize the need for careful water management after applications.

Nutrient and pesticide remediation using a two-stage bioreactor-adsorptive system under two hydraulic retention times.

Nutrients and pesticides in agricultural runoff contribute to the degradation of water resources. Nitrates and phosphates can be remediated through the use of treatment systems such as woodchip bioreactors and adsorbent aggregate filters; however, concerns remain over potential effects of pesticides on nutrient removal efficiency in these systems. To test this, we designed laboratory-scale woodchip bioreactors equipped with secondary adsorbent aggregate filters and investigated the capacity of these systems to remediate nutrients when operated under two hydraulic retention times (HRT) and in the presence of commonly used pesticides. The woodchip bioreactors effectively removed over 99% of nitrate per day when operated under a 72 h hydraulic retention time, with the secondary expanded shale aggregate filters consistently reducing phosphate concentrations by 80-87%. Treatment efficacy of both systems was maintained in the presence of the insecticide chlorpyrifos. Reducing HRT in the bioreactors to 21 min decreased nitrate removal efficiency; however, the insecticides bifenthrin, chlorpyrifos, and the herbicide oxyfluorfen were reduced by 76%, 63%, and 31%, respectively. Cultivation approaches led to the isolation of 45 different species from the woodchip bioreactors operated under a 21 min HRT, with Bacillus species being the most prevalent throughout the treatment. By contrast, pesticide application decreased the number and diversity of Bacillus isolates and enriched for Pseudomonas and Exiguobacterium species. Woodchip bioreactors and adsorbent aggregate filters provide effective treatment platforms to remediate agrochemicals, where they maintain treatment efficacy in the presence of pesticides and can be modulated through HRT management to achieve environmental and operational water quality goals.

Pesticide Sorption to Soilless Media Components Used for Ornamental Plant Production and Aluminum Water Treatment Residuals.

Commercial producers of containerized ornamental plants almost exclusively use soilless media as the substrate for growing the plants. Soilless media are composed primarily of organic materials as opposed to mineral soils. Significant amounts of pesticides can leach from pots containing soilless media to which pesticides have been added as drenches or top-dressings. One of the goals of this project was to identify whether individual components comprising soilless media have differing affinities for the pesticides acephate, imidacloprid, metalaxyl, and plant growth regulator paclobutrazol. One-point 24 h equilibrium sorption assays were conducted to characterize sorption of the pesticides to sand, perlite, vermiculite, coir, peat, pine bark, and aluminum-water treatment residuals (Al-WTRs). Five-point isotherms were then constructed for the more sorptive peat and pine bark substrate components, and for the Al-WTRs. Results indicated significant differences in pesticide behavior with each substrate. Sorption of acephate to most of the substrate components was relatively low, comprising 21-31% of the initial amounts for soilless media components and 63% in Al-WTRs. Al-WTRs were highly sorptive for imidacloprid as evidenced by a partition coefficient of K F = 3275.4 L kg-1. Pine bark was the most sorptive for metalaxyl-M with a measured K F = 195.0 L kg-1. Peat had the highest affinity for paclobutrazol (K F = 398.4 L kg-1). These results indicate that none of component of soilless media has a universally high attraction for all of the pesticides studied.

Micropollutants in groundwater from septic systems: Transformations, transport mechanisms, and human health risk assessment.

Septic systems may contribute micropollutants to shallow groundwater and surface water. We constructed two in situ conventional drainfields (drip dispersal and gravel trench) and an advanced drainfield of septic systems to investigate the fate and transport of micropollutants to shallow groundwater. Unsaturated soil-water and groundwater samples were collected, over 32 sampling events (January 2013 to June 2014), from the drainfields (0.31-1.07 m deep) and piezometers (3.1-3.4 m deep). In addition to soil-water and groundwater, effluent samples collected from the septic tank were also analyzed for 20 selected micropollutants, including wastewater markers, hormones, pharmaceuticals and personal care products (PPCPs), a plasticizer, and their transformation products. The removal efficiencies of micropollutants from septic tank effluent to groundwater were similar among three septic systems and were 51-89% for sucralose and 53->99% for other micropollutants. Even with high removal rates within the drainfields, six PPCPs and sucralose with concentrations ranging from <0.3 to 154 ng/L and 121 to 32,000 ng/L reached shallow groundwater, respectively. The human health risk assessment showed that the risk to human health due to consumption of groundwater is negligible for the micropollutants monitored in the study. A better understanding of ecotoxicological effects of micropollutant mixtures from septic systems to ecosystem and human health is warranted for the long-term sustainability of septic systems.

Effects of a larval mosquito biopesticide and Culex larvae on a freshwater nanophytoplankton (Selenastrum capricornatum) under axenic conditions.

The effects of microbial biopesticides used for mosquito control on autotrophic microorganisms such as nanophytoplankton are equivocal. We examined impacts of mosquito biopesticides and mosquito larvae on primary producers in two independent experiments. In the first experiment, we examined the effects of a commonly used microbial biopesticide formulation (VectoMax® CG) on a unicellular microalga, Selenastrum capricornatum Printz, under axenic laboratory conditions. The biopesticide treatments included two concentrations (0.008 and 0.016 g liter-1 ) of VectoMax® CG and two controls (one untreated and another with autoclaved 0.016 g VectoMax® CG liter-1 ) in replicated axenic experimental microcosms. Spectrophotometric analysis of chlorophyll a (proxy for algal biomass) and direct enumeration of algal cells following the treatments revealed no significant effects of the microbial biopesticide on algal population growth during the four-week study. In the second experiment, we tested the effects of different densities of Culex larvae on the population of S. capricornatum. Effects of mosquito larvae feeding on S. capricornatum were significant with a curvilinear relationship between larval density and algal abundance in the water column. Together, these studies demonstrated a lack of direct cytological/toxicological effects of Bacillus-based microbial pesticides on freshwater primary production and support the hypothesis that the reduction in algal primary production previously reported when Bti products were applied to aquatic environments was likely independent of the Bacillus-based larvicidal toxins. Instead, it was likely mediated by microbial interactions in the water column and the trophic cascade effects that resulted from the removal of larval mosquitoes. These studies suggest that mosquito larvae independent of pesticide application can influence primary production. Our method of evaluating biopesticides against small photoautotrophs can be very useful for studying the unintended effects on autotrophic microorganisms of other pesticides, including herbicides and pesticides applied to aquatic environments.

Septic systems as hot-spots of pollutants in the environment: Fate and mass balance of micropollutants in septic drainfields.

Septic systems, a common type of onsite wastewater treatment systems, can be an important source of micropollutants in the environment. We investigated the fate and mass balance of 17 micropollutants, including wastewater markers, hormones, pharmaceuticals and personal care products (PPCPs) in the drainfield of a septic system. Drainfields were replicated in lysimeters (1.5m length, 0.9m width, 0.9m height) and managed similar to the field practice. In each lysimeter, a drip line dispersed 9L of septic tank effluent (STE) per day (equivalent to 32.29L/m(2) per day). Fourteen micropollutants in the STE and 12 in the leachate from drainfields were detected over eight months. Concentrations of most micropollutants in the leachate were low (<200ng/L) when compared to STE because >85% of the added micropollutants except for sucralose were attenuated in the drainfield. We discovered that sorption was the key mechanism for retention of carbamazepine and partially for sulfamethoxazole, whereas microbial degradation likely attenuated acetaminophen in the drainfield. This data suggests that sorption and microbial degradation limited transport of micropollutants from the drainfields. However, the leaching of small amounts of micropollutants indicate that septic systems are hot-spots of micropollutants in the environment and a better understanding of micropollutants in septic systems is needed to protect groundwater quality.

Occurrence and ecological risks from fipronil in aquatic environments located within residential landscapes.

This study investigated the occurrence of fipronil and its metabolites in aquatic environments in residentially-developed landscapes, including five canals and three retention ponds. Fipronil was detected at four of the sites, with concentrations of 0.5-207.3 ng L(-1). Fipronil sulfone and fipronil sulfide were detected at three sampling sites, with concentrations ranging from 0.46 to 57.75 and 0.40-26.92 ng L(-1), respectively. Multiple risk assessment methods were performed to characterize potential ecological risks, including deterministic screening and probabilistic risk assessment techniques. The deterministic method indicated no risk to certain biotic groups (i.e. aquatic plants, fish, molluscs, and algae-moss-fungi), but did indicate risks to larval insects and crustaceans. Results from the probabilistic risk assessment indicated significant ecological risks (acute and chronic) ranging from 0.75 to 58.9% and 3.9-35.0% when organisms were exposed to the maximum and median concentrations detected, respectively. The potentially affected fraction of species (PAF) likely to be acutely impacted ranged from 4.6 to 8.1% (fipronil), 0.2-1.6% (fipronil sulfone), and 1.9-3.1% (fipronil sulfide) in the ponds with frequent detectable concentrations. The PAF likely to be impacted at chronic toxicity levels ranged from 16.5 to 23.8% for fipronil. Joint probability curve analysis indicated that concentrations exceeded the LC50 of the most sensitive 5% of species 8.5-18.8% of the time at two of the sites with the most frequent detections. Using the more conservative NOEC/LOEC values, there was a 75-78% probability that concentrations were high enough to negatively affect the most sensitive 5% of species at the same two sites, indicating significant risks for chronic toxicity. JPCs indicated a ≤2.6% probability of fipronil sulfone exceeding the LC50 concentrations for the most sensitive 5% of species at the same two sites; and a 4.3-6.8% probability of fipronil sulfide exceeding the LC50 concentrations at the same sites. Results indicate that fipronil and its sulfone and sulfide degradation products may present significant risks to aquatic organisms in some residentially-developed areas.

Uptake and distribution of bisphenol A and nonylphenol in vegetable crops irrigated with reclaimed water.

The potential uptake and distribution of bisphenol A (BPA) and nonylphenol (NP) (from reclaimed irrigation water) in edible crops was investigated. BPA and NP were spiked into simulated reclaimed water at environmentally relevant concentrations. Two crops (lettuce, Lactuca sativa and tomato, Lycopersicon esculentum) were grown hydroponically in a greenhouse using the spiked irrigation water under two irrigation exposure scenarios (overhead foliar exposure and subsurface root exposure). BPA concentrations in tomato fruit were 26.6 ± 5.8 (root exposure) and 18.3 ± 3.5 (foliar exposure) µg kg(-1), while concentrations in lettuce leaves were 80.6 ± 23.1 (root exposure) and 128.9 ± 17.4 (foliar exposure) µg kg(-1). NP concentrations in tomato fruit were 46.1 ± 6.6 (root exposure) and 24.6 ± 6.4 (foliar exposure) µg kg(-1), while concentrations in lettuce leaves were 144.1 ± 9.2 (root exposure) and 195.0 ± 16.9 (foliar exposure) µg kg(-1). BPA was relatively mobile in lettuce plants regardless of exposure route. Limited mobility was observed for NP in both crops and BPA in tomatoes. The estimated daily intake of BPA and NP through consumption of vegetables irrigated with reclaimed water ranged from 8.9-62.9 to 11.9-95.1 µg, respectively, depending on the exposure route.

Toxicity of fipronil to the midge, Cricotopus lebetis Sublette.

Fipronil, a relatively new insecticide more recently developed than organophosphates and pyrethroids, has been detected in surface water draining from agricultural and urban-developed areas. This insecticide is primarily lost through subsurface and surface drainage from terrestrial areas where it has been applied. Invasive aquatic plants often need to be managed in these receiving water bodies to prevent loss of recreational and functional values (e.g., drainage), especially in subtropical and tropical areas. One insect of particular interest is the chironomid midge Cricotopus lebetis Sublette, which may be a useful augmentative biocontrol agent for the invasive aquatic weed Hydrilla verticillata L.f. Royale. Exposure of aquatic organisms, especially insects, to fipronil may significantly impact nontarget populations. These studies investigated the sensitivity of C. lebetis to fipronil exposures ranging from 24 to 96 h. The LC50 observed for each exposure interval was 7.26 µg/L (24 h), 2.61 µg/L (48 h), 1.78 µg/L (72 h), and 1.06 µg/L (96 h). The LC90 values observed were 47.18 µg/L (24 h), 9.55 µg/L (48 h), 6.45 µg/L (72 h), and 4.81 µg/L (96 h). Behavioral changes were seen at all fipronil concentration levels, where larvae exited the plant and exhibited abnormal behavior, such as restricted movement and lack of feeding. Results indicate that acute lethality occurred at environmentally relevant concentrations of fipronil.

Influence of exposure concentration and duration on effects and recovery of Lemna minor exposed to the herbicide norflurazon.

This study evaluated the effects and potential recovery of the surrogate aquatic macrophyte Lemna minor exposed to the herbicide norflurazon for 10 days under controlled conditions. Decreases in frond production occurred as early as 2 days after treatment (DAT) at concentrations ≥250 µg/L. The observed no observable-adverse effects and lowest observable-adverse effects concentrations during the 2-, 6-, and 10-day exposure periods were 100/250, 10/25, and 10/25 µg/L, respectively, for total frond production. The estimated EC(50) value for total frond production was 24.9 ± 4.1 µg/L (6 days of exposure). Symptoms of norflurazon toxicity (bleaching of foliage) were apparent within 2 DAT for concentrations ≥25 µg/L with 30-39 % of the fronds within each treatment exhibiting symptoms of toxicity. After 6- and 10-day exposures, 69-77 and 80-95 % of these plants showed toxic symptoms, respectively. Symptoms of toxicity for the 10 µg/L treatment first appeared at 4 DAT (51 % of fronds were symptomatic), peaked at 91 % 8 DAT, and were only 2 % at 10 DAT, thus indicating recovery. Norflurazon toxicity was eventually reversible at all concentrations once it was removed from the nutrient solutions. After 17 days of recovery (27 DAT), growth rates for all concentrations ≤250 µg/L were similar to those of the controls. Growth rates for all treatment concentrations recovered to control levels after 28 days of recovery (38 DAT).

Analysis of bisphenol A, nonylphenol, and natural estrogens in vegetables and fruits using gas chromatography-tandem mass spectrometry.

Bisphenol A (BPA), nonylphenol (NP), and steroidal estrogens in vegetables and fruits were analyzed using gas chromatography with tandem mass spectrometry (GC-MS/MS). Isotope dilution standards were spiked before the extraction to account for extraction inefficiency and loss of analytes during sample workup. Recoveries were >90% for all of the compounds in each matrix. The limit of detection (LOD) ranged from 0.03 to 0.3 µg kg(-1), whereas the limit of quantitation (LOQ) ranged from 0.1 to 1.0 µg kg(-1). All analytes can be monitored in a single GC-MS/MS run with a run time of 20 min. Occurrence of these endocrine-disrupting chemicals (EDCs) in vegetables and fruits from local markets was observed using the established analytical method. BPA was detected in all vegetable and fruit samples, ranging from 0.2 ± 0.1 to 9.0 ± 4.9 µg kg(-1), indicating significant exposure potential for humans. NP was detected in pumpkin, sweet potato, citrus, and apple samples. The concentration of 4-n-NP ranged from 5.3 ± 2.4 to 18.9 ± 8.0 µg kg(-1), whereas that of 4-NP ranged from 5.1 ± 2.6 to 12.2 ± 3.6 µg kg(-1). Concentrations of 17-ß-estradiol in vegetables and fruits ranged from 1.3 ± 0.4 to 2.2 ± 1.0 µg kg(-1) except those in tomato and strawberry, in which no 17-ß-estradiol was detected. The estimated daily intake of 17-ß-estradiol was beyond the recommended acceptable daily intake (ADI) for children as recommended by the Joint FAO/WHO Expert Committee on Food Additives (JECFA).

Scenario analysis for sustainable development of Chongming Island: water resources sustainability.

With the socioeconomic and urban development of Chongming Island (the largest alluvial island in the world), water demand is rapidly growing. To make adjustments to the water utilization structure of each industry, allocate limited water resources, and increase local water use efficiency, this study performed a scenario analysis for the water sustainability of Chongming Island. Four different scenarios were performed to assess the water resource availability by 2020. The growth rate for water demand will be much higher than that of water supply under a serious situation prediction. The water supply growth volume will be 2.22 × 10(8)m(3) from 2010 to 2020 under Scenario I and Scenario II while the corresponding water demand growth volume will be 2.74 × 10(8)m(3) and 2.64 × 10(8)m(3), respectively. There will be a rapid growth in water use benefit under both high and low development modes. The water use benefit will be about 50 CNY/m(3) under Scenarios I and II in 2020. The production structure will need to be adjusted for sustainable utilization of water resources. Sewage drainage but not the forest and grass coverage rate will be a major obstacle to future development and environmental quality. According to a multi-level fuzzy comprehensive evaluation, Scenario II is finally deemed to be the most desirable plan, suggesting that the policy of rapid socioeconomic development and better environmental protection may achieve the most sustainable development of Chongming Island in the future.

Copper losses in surface runoff from flatwoods citrus production areas.

Crop production in areas with a high water table and poorly drained soils requires special drainage infrastructure to allow adequate rooting depth. In addition to facilitating drainage, this infrastructure also facilitates discharge of agrichemicals dissolved in drainage and runoff water. Copper export from bedded citrus production areas was evaluated using simulated rainfall events following application of copper. Copper concentrations in runoff water from individual water furrows ranged from 13 to 223 µg/L during the staged events, while copper loadings ranged from 32 to 302 g/water furrow.

Characterization of selected organo-nitrogen herbicides in South Florida canals: exposure and risk assessments.

Much uncertainty exists regarding the discharge characteristics of terrestrial-use herbicides into aquatic systems. This study evaluated the temporal distribution and concentrations of five commonly used herbicides (atrazine, bromacil, metolachlor, norflurazon, and simazine) in a typical South Florida watershed. Surface water samples were collected weekly over a 3-yr period from four canals and Ten Mile Creek. These systems received drainage water from a variety of land-uses, including residential, pastures, and citrus production. Herbicides were extracted and analyzed by GC-MS/SIM. Atrazine was most frequently detected (87% of samples) in the canal serving the residentially developed sub-basin, with median and maximum concentrations of 0.43 and 6.67 µg L(-1), respectively. Norflurazon was most frequently detected (90-95% of samples) in the systems serving agricultural production areas, with median and maximum concentrations ranging from 0.37-0.63 µg L(-1) and 1.98-6.97 µg L(-1), respectively. Bromacil was detected in 14-36% of samples with median and maximum concentrations ranging from 0.50-0.67 µg L(-1) and 2.31-4.96 µg L(-1), respectively. Metolachlor was detected in 1.8-10% of the samples, with median and maximum concentrations ranging from 0.16-0.2 µgL(-1) and 0.17-1.55 µg L(-1), respectively. Simazine was detected in 10-35% of the samples, with median and maximum concentrations ranging from 0.18-0.28 µg L(-1) and 0.37-1.35 µg L(-1), respectively. Bromacil+norflurazon was the most commonly detected (240 samples of 1060 total) binary combination of herbicides; whereas bromacil+norflurazon+simazine was the most frequently detected tertiary combination (58 samples). While detectable concentrations were present for significant periods of time, risks of acute toxicity were relatively low; affecting <1% of the potentially affected fraction (PAF) of plant species based on 90th centile exposure concentrations and 10th centile effects concentrations from species sensitivity distributions.

Acid tolerance of an acid mine drainage bioremediation system based on biological sulfate reduction.

The acid tolerance response of an AMD bioremediation system based on sulfate reduction was investigated. Efficient sulfate reduction was observed with a maximum sulfate reduction rate of 12.3±0.8 mg L(-1) d(-1) and easily available organic carbon was released during high acid treatment with an initial pH of 2.0. The rapid increase in sulfate reduction was observed when the extreme acid treatment with an initial pH of 1.0 was stopped. Column experiment on acid shock showed that efficient sulfate reduction was maintained while precipitation of Cu or Zn still occurred during extreme or high acid shock. More than 98% of Cu and 85% of Zn were removed in the high acid column experiment with influent pH of 2.0. The majority bacteria in the remediation system used for high acid drainage belonged to genera Clostridiaceae, Eubacterium, Pseudobutyrivibrio, and Clostridium. These findings showed high acid tolerance of the straw remediation system.

Norflurazon and simazine removal from surface water using a constructed wetland.

Norflurazon and simazine are pre-emergent herbicides detected frequently in surface water associated with South Florida agricultural canals and drainage water. This study investigated the potential use of a 1.34 ha constructed wetland for removing these herbicides from surface water. The total length of the wetland was 400 m and width was 35 m. A surface water flow rate of 740 L/min was maintained in the system using a pump. The plant community within the system consisted primarily of Panicum repens, Alternanthera philoxeroides, and Bacopa caroliniana. Norflurazon and simazine, derived from commercial formulations, were injected (51.1 g active ingredient each) directly into the water pumped into the wetland over a 2 h period. Water samples were collected from the wetland upstream of the dosing system at 3 h intervals from the beginning through 360 h and at the exit point at 1, 2, and 3 h intervals for the periods of 0-24, 25-48 and 49-360 h after dosing, respectively. The herbicides were extracted using C-18 cartridges and were analyzed by GC-TSD. The total mass of each herbicide discharged from the system was estimated by multiplying the concentration by the total volume discharged during the sampled period. Neither herbicide was detected in the inflow water during the entire study. Norflurazon was first detected at the exit 19 h after dosing and simazine after 23 h. Discharge patterns of the two herbicides differed dramatically. Norflurazon tended to bleed off from the wetland with no distinct peak concentration. However, the mobile fraction of simazine was discharged over a 58 h period. Mean/maximum/median detectable concentrations of the herbicides were 3.9 ± 1.7/8.1/3.4 µg L(-1) for norflurazon, and 11.9 ± 6.8/23.6/12.0 µg L(-1) for simazine, respectively. The total masses of norflurazon and simazine discharged from the exit during the 15 day study were 51.7 and 26.9 g, indicating 0% and 47.4% removal from the surface water by the system.