•Fate of current-use pesticides in an agricultural estuary is documented.•Pesticide application corresponded to maximum in-stream pesticide concentrations.•Relationship in bed sediment pesticide ...concentrations and distance from source.•Fish and crabs accumulate current-use pesticides, including fungicides.•First report on the occurrence and accumulation of fungicides in tissue.
The current study documents the fate of current-use pesticides in an agriculturally-dominated central California coastal estuary by focusing on the occurrence in water, sediment and tissue of resident aquatic organisms. Three fungicides (azoxystrobin, boscalid, and pyraclostrobin), one herbicide (propyzamide) and two organophosphate insecticides (chlorpyrifos and diazinon) were detected frequently. Dissolved pesticide concentrations in the estuary corresponded to the timing of application while bed sediment pesticide concentrations correlated with the distance from potential sources. Fungicides and insecticides were detected frequently in fish and invertebrates collected near the mouth of the estuary and the contaminant profiles differed from the sediment and water collected. This is the first study to document the occurrence of many current-use pesticides, including fungicides, in tissue. Limited information is available on the uptake, accumulation and effects of current-use pesticides on non-target organisms. Additional data are needed to understand the impacts of pesticides, especially in small agriculturally-dominated estuaries.
AbstractAn accurate estimation of the jacking forces likely to be experienced during microtunnelling is a key design concern for the structural capacity of pipe segments, the location of intermediate ...jacking stations, and the efficacy of the pipe-jacking project itself. This paper presents a Bayesian updating approach for the prediction of jacking forces during microtunnelling. The proposed framework was applied to two pipe-jacking case histories completed in the United Kingdom: a 275-m drive in silt and silty sand, and a 1,237-m drive in mudstone. To benchmark the Bayesian predictions, a classical optimization technique, namely genetic algorithms, is also considered. The results show that predictions of pipe-jacking forces using the prior best estimate of model input parameters provided a significant overprediction of the monitored jacking forces for both drives. This highlights the difficulty of capturing the complex geotechnical conditions during tunnelling within prescriptive design approaches and the importance of robust back-analysis techniques. Bayesian updating was shown to be a very effective option, in which significant improvements in the mean predictions and associated variance of the total jacking force are obtained as more data are acquired from the drive.
A statewide investigation of urban creek sediment toxicity was conducted in California in recognition of increased incidences of toxicity linked to pyrethroid pesticides. The goals were to examine ...the spatial occurrence and magnitude of sediment toxicity in California urban creeks, and to examine the role of pyrethroids in toxic urban creek sediment samples. After a preliminary screening of 90 sites, 30 creeks were sampled in eight geographical regions. Sediment toxicity was assessed using 10 day bioassays with the resident amphipod Hyalella azteca. Bioassays were conducted at two test temperatures of 23 °C and at 15 °C to provide evidence of the cause of toxicity, and to more accurately reflect ambient environmental temperatures. Twenty-five of 30 samples were toxic when tested at 23 °C, and all 30 samples were toxic when tested at 15 °C. The magnitude of toxicity increased in samples tested at 15 °C suggesting the influence of pyrethroids, which are more toxic at colder temperatures. Pyrethroids were present in all sediment samples and were the only compounds detected at concentrations toxic to H. azteca. Bifenthrin was the pyrethroid of greatest toxicological concern, occurring in all 30 samples at concentrations up to 219 ng/g. Pyrethroid contamination of urban creeks was most severe in the Los Angeles, Central Valley, and San Diego regions, respectively. However, pyrethroids were also linked to urban creek aquatic toxicity in all regions sampled, including the less urbanized areas of the North Coast and Lake Tahoe.
Organism tolerance thresholds for emerging contaminants are vital to the development of water quality criteria. Acute (96-h) and chronic (10-day) effects thresholds for neonicotinoid pesticides ...clothianidin and thiamethoxam, and the carbamate pesticide methomyl were developed for the midge
Chironomus dilutus
to support criteria development using the UC Davis Method. Median lethal concentrations (LC50s) were calculated for acute and chronic exposures, and the 25% inhibition concentrations (IC25) were calculated for the chronic exposures based on confirmed chemical concentrations. Clothianidin effect concentrations were 4.89 µg/L, 2.11 µg/L and 1.15 µg/L for 96-h LC50, 10-day LC50 and 10-day IC25, respectively. Similarly, thiamethoxam concentrations were 56.4 µg/L, 32.3 µg/L and 19.6 µg/L, and methomyl concentrations were 244 µg/L, 266 µg/L and 92.1 µg/L. Neonicotinoid effect concentrations compared favorably to previously published 96-h and 14-day LC50 concentrations, and methomyl effect concentrations were within the acute survival range reported for
Chironomus
species and other organisms.
Several classes of pesticides have been shown to impair water quality in California, including organophosphates, pyrethroids and neonicotinoids. Vegetative treatment systems (VTS) can reduce ...pesticide loads and associated toxicity in agricultural runoff, but many water-soluble pesticides such as neonicotinoids are not effectively treated by VTS, and VTS installation is not always an option for growers required to remove non-crop vegetation for food safety concerns. Recent studies have shown that biochar filtration can be used to remove soluble contaminants, especially when coupled with other VTS components. We evaluated a mobile carbon filter system consisting of a trailer-mounted tank containing approximately 600L (~ 180 kg) of biochar. Input water from a 437-hectare agricultural drainage was pre-filtered and treated with biochar during two multi-week study periods. Laboratory toxicity tests and chemical and nutrient analyses were conducted on input and output water. Pesticide concentrations were initially reduced by greater than 99%. Treatment efficacy declined linearly and was expected to remain at least 50% effective for up to 34 weeks. Toxicity was assessed with
Ceriodaphnia dubia
,
Hyalella azteca
and
Chironomus dilutus
. Significant input toxicity was reduced to non-toxic levels in 6 of 16 samples. Some input concentrations of the neonicotinoid imidacloprid and the pyrethroid cypermethrin exceeded organism-specific toxicity thresholds and benchmarks, but the overall causes of toxicity were complex mixtures of agricultural chemicals. Nutrients were not reduced by the biochar. Results demonstrate the utility of biochar in treating agricultural runoff and provide measures of the longevity of biochar under field conditions.
Pesticide loads and associated toxicity can be significantly reduced using integrated vegetated treatment systems, which remove moderately soluble and hydrophobic pesticides, but need a sorbent ...material to remove more soluble pesticides. Neonicotinoids such as imidacloprid are widely used insecticides, acutely toxic, and have been linked to a range of ecological effects. Laboratory experiments were conducted to test the sorptive capacity of granulated activated carbon and biochar for removing imidacloprid and the organophosphate insecticide chlorpyrifos in a scaled-down treatment system. Simulated irrigation water spiked with individual pesticides was treated with a bench-top system designed to mimic a 600 L carbon installation receiving 108,000 L of flow per day for sixteen days. Biochar reduced insecticides to less than detectable and non-toxic levels. Granulated activated carbon similarly reduced chlorpyrifos, but allowed increasing concentrations of imidacloprid to break through. Both media treated environmentally relevant concentrations, and would be effective if used under conditions with reduced particle loads.
The Salinas Valley in Monterey County, California, USA, is a highly productive agricultural region. Irrigation runoff containing pesticides at concentrations toxic to aquatic organisms poses a threat ...to aquatic ecosystems within local watersheds. This study monitored the effectiveness of a constructed wetland treatment system with a granulated activated carbon (GAC) filter installation at reducing pesticide concentrations and associated toxicity to
Ceriodaphnia dubia
,
Hyalella azteca
, and
Chironomus dilutus
. The wetland was supplied with water pumped from an impaired agricultural and urban drainage. Across five monitoring trials, the integrated system’s average pesticide concentration reduction was 52%. The wetland channel and GAC filtration components individually provided significant treatment, and within each, pesticide solubility had a significant effect on changes in pesticide concentrations. The integrated treatment system also reduced nitrate by 61%, phosphate by 73%, and turbidity by 90%. Input water was significantly toxic to
C. dubia
and
H. azteca
in the first trial. Toxicity to
C. dubia
persisted throughout the system, whereas toxicity to
H. azteca
was removed by the channel, but there was residual toxicity post-GAC. The final trial had significant input toxicity to
H. azteca
and
C. dilutus
. The channel reduced toxicity to
H. azteca
and removed toxicity to
C. dilutus
. GAC filtration reduced
H. azteca
toxicity to an insignificant level. There was no input toxicity in the other three trials. The results demonstrate that a wetland treatment system coupled with GAC filtration can reduce pesticide concentrations, nutrients, suspended particles, and aquatic toxicity associated with agricultural runoff.
California's Stream Pollution Trends program (SPoT) assesses long-term water quality trends, using 100 base-of-the-watershed sampling sites. Annual statewide sediment surveys from 2008 to 2012 ...identified consistent levels of statewide toxicity (19%), using the freshwater amphipod Hyalella azteca. Significant contaminant trends included a decrease in PCBs, stable concentrations of metals and PAHs, and a statewide increase in detections and concentrations of pyrethroid pesticides. The pyrethroid pesticide bifenthrin was detected in 69% of samples (n = 410). Detection of toxicity increased in a subset of samples tested at a more environmentally relevant test temperature (15 °C), and the magnitude of toxicity was much greater, indicating pyrethroid pesticides as a probable cause. Pyrethroid toxicity thresholds (LC50) were exceeded in 83% of samples with high toxicity. Principal components analysis related pyrethroids, metals and total organic carbon to urban land use.
•Toxicity and contaminant concentrations were higher in urban dominated watersheds.•Average and range of total pyrethroid concentrations increased between 2008 and 2012.•Pyrethroid toxicity thresholds (LC50) were exceeded in 83% of samples with high toxicity.
Detections and concentrations of current use pesticides are increasing in California urban watersheds, while legacy organochlorine contaminants are decreasing statewide.
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