Measured Concentrations of Herbicides and Model Predictions of Atrazine Fate in the Patuxent River Estuary (original) (raw)
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CBM - Cahiers de Biologie Marine, 2006
Our study aims at making progress the estimate of herbicide and nutrient inputs to the Marennes-Oleron bay which could influence summer oysters mortalities, and to bring a better understanding of the impact on coastal ecosystems by modelling the dynamics of these compounds in the shellfish-farming area. The development of a strategy adapted to the river Charente and its estuary reveals that agricultural activity on the watershed area is omnipresent, as well on the level of the nitrogen as on the one of herbicides contributions. It is thus necessary to specify Charente fluxes, which is the main tributary of the Marennes-Oleron bay, in order to better characterize its impact on shellfish-farming activity. Hydrodynamic modelling will constitute an invaluable help in the risk assessment with respect to pesticides, by specifying the periods of the high and low concentrations of these molecules and the biotope exposure durations.
Herbicide Transport in Goodwater Creek ExperimentalWatershed: I. Long-Term Research on Atrazine1
JAWRA Journal of the American Water Resources Association, 2011
Atrazine continues to be the herbicide of greatest concern relative to contamination of surface waters in the United States (U.S.). The objectives of this study were to analyze trends in atrazine concentration and load in Goodwater Creek Experimental Watershed (GCEW) from 1992 to 2006, and to conduct a retrospective assessment of the potential aquatic ecosystem impacts caused by atrazine contamination. Located within the Central Claypan Region of northeastern Missouri, GCEW encompasses 72.5 km 2 of predominantly agricultural land uses, with an average of 21% of the watershed in corn and sorghum. Flow-weighted runoff and weekly base-flow grab samples were collected at the outlet to GCEW and analyzed for atrazine. Cumulative frequency diagrams and linear regression analyses generally showed no significant time trends for atrazine concentration or load. Relative annual loads varied from 0.56 to 14% of the applied atrazine, with a median of 5.9%. A cumulative vulnerability index, which takes into account the interactions between herbicide application, surface runoff events, and atrazine dissipation kinetics, explained 63% of the variation in annual atrazine loads. Based on criteria established by the U.S. Environmental Protection Agency, atrazine reached concentrations considered harmful to aquatic ecosystems in 10 of 15 years. Because of its vulnerability, atrazine registrants will be required to work with farmers in GCEW to implement practices that reduce atrazine transport.
Modeling pesticide fate in a small tidal estuary
Ecological Modelling, 2007
Atrazine Metolachlor EXAMS Modeling Water quality Estuaries a b s t r a c t The exposure analysis modeling system (EXAMS), a pesticide fate model developed by the U.S. Environmental Protection Agency, was modified to model the fate of the herbicides atrazine and metolachlor in a small tidally dominated estuary (Bath Creek) in North Carolina, USA where freshwater inflow accounts for only 3% of the total flow. The modifications simulated the changes that occur during the tidal cycle in the estuary, scenarios that are not possible with the original EXAMS model. Two models were created within EXAMS, a steadystate model and a time-variant tidally driven model. The steady-state model accounted for tidal flushing by simply altering freshwater input to yield an estuary residence time equal to that measured in Bath Creek. The tidal EXAMS model explicitly incorporated tidal flushing by modifying the EXAMS code to allow for temporal changes in estuary physical attributes (e.g., volume). The models were validated with empirical measurements of atrazine and metolachlor concentrations in the estuary shortly after herbicide application in nearby fields and immediately following a rain event. Both models provided excellent agreement with measured concentrations. The steady-state EXAMS model accurately predicted atrazine concentrations in the middle of the estuary over the first 3 days and under-predicted metolachlor by a factor of 2-3. The time-variant, tidally driven EXAMS model accurately predicted the rise and plateau of both herbicides over the 6-day measurement period. We
Environmental and human health risk indicators for agricultural pesticides in estuaries
Ecotoxicology and environmental safety, 2018
The present study aims to contribute to a better assessment of pesticide environmental and human health (here evaluated in the context of human exposure via food items) risks for the estuarine system by comprehensively studying the spatial and temporal occurrence of the pesticides atrazine, azoxystrobin, bentazon, λ-cyhalothrin, penoxsulam and terbuthylazine in the River Mondego estuary (Portugal). Pesticide quantification was performed in surface water, sediment, macroalgae (Ulva spp., Gracilaria gracilis, Fucus vesiculosus), aquatic plants (Zostera noltii, Spartina maritime, Scirpus maritimus) and bivalves (Scrobicularia plana). Since intense precipitation could promote the runoff of pesticides from the surrounding agricultural fields, a single long-duration flood event was also studied in this estuarine system. Under normal flow conditions, quantified concentrations were determined mostly during summer in agreement with the pesticide application period. Azoxystrobin presented the...
Herbicide Persistence in Seawater Simulation Experiments
PLOS ONE, 2015
Herbicides are detected year-round in marine waters, including those of the World Heritage listed Great Barrier Reef (GBR). The few previous studies that have investigated herbicide persistence in seawater generally reported half-lives in the order of months, and several studies were too short to detect significant degradation. Here we investigated the persistence of eight herbicides commonly detected in the GBR or its catchments in standard OECD simulation flask experiments, but with the aim to mimic natural conditions similar to those found on the GBR (i.e., relatively low herbicide concentrations, typical temperatures, light and microbial communities). Very little degradation was recorded over the standard 60 d period (Experiment 1) so a second experiment was extended to 365 d. Half-lives of PSII herbicides ametryn, atrazine, diuron, hexazinone and tebuthiuron were consistently greater than a year, indicating high persistence. The detection of atrazine and diuron metabolites and longer persistence in mercuric chloride-treated seawater confirmed that biodegradation contributed to the breakdown of herbicides. The shortest half-life recorded was 88 d for growth-regulating herbicide 2,4-D at 31°C in the dark, while the fatty acid-inhibitor metolachlor exhibited a minimum half-life of 281 d. The presence of moderate light and elevated temperatures affected the persistence of most of the herbicides; however, the scale and direction of the differences were not predictable and were likely due to changes in microbial community composition. The persistence estimates here represent some of the first appropriate data for application in risk assessments for herbicide exposure in tropical marine systems. The long persistence of herbicides identified in the present study helps explain detection of herbicides in nearshore waters of the GBR year round. Little degradation of these herbicides would be expected during the wet season with runoff and associated flood plumes transporting a high proportion of the original herbicide from rivers into the GBR lagoon.
Ecotoxicology (London, England), 2018
Estuaries, coastal lagoons and other transition ecosystems tend to become the ultimate reservoirs of pollutants transported by continental runoff, among which pesticides constitute the class of most concern. High amounts of dissolved and particulated organic matter greatly contribute to the accumulation of pesticides that eventually become trapped in sediments or find their way along food chains. Perhaps not so surprisingly, it is common to find elevated levels of pesticides in estuarine sediments decades after their embargo. Still, it remains challenging to address ecotoxicity in circumstances that invariably imply mixtures of contaminants and multiple factors affecting bioavailability. Despite advances in methods for detecting pesticides in waters, sediments and organisms, chemical data alone are insufficient to predict risk. Many researchers have been opting for ex situ bioassays that mimic the concentrations of pesticides in estuarine waters and sediments using a range of ecolog...
The Effect of Atrazine on Louisiana Gulf Coast Estuarine Phytoplankton
Archives of environmental contamination and toxicology, 2017
Pesticides may enter water bodies in areas with a high proportion of agricultural land use through surface runoff, groundwater discharge, and erosion and thus negatively impact nontarget aquatic organisms. The herbicide atrazine is used extensively throughout the Midwest and enters the Mississippi River through surface runoff and groundwater discharge. The purpose of this study was to determine the extent of atrazine contamination in Louisiana's estuaries from Mississippi River water under different flow and nutrient regimes (spring and summer) and its effect on the biomass and oxygen production of the local phytoplankton community. The results showed that atrazine was consistently present in these systems at low levels. Microcosm experiments exposed to an atrazine-dilution series under low and high nutrient conditions to determine the phytoplankton stress response showed that high atrazine levels greatly decreased phytoplankton biomass and oxygen production. Phytoplankton expos...
Science of The Total Environment, 2020
Multivariate analysis Agricultural landcover Chesapeake Bay watershed landcover in the immediate catchment, as well as stream discharge, did not have a significant effect on the occurrence probabilities of most compounds. Four pesticides (atrazine, metolachlor, fipronil and simazine) cooccurred across sites after accounting for environmental covariates. These results provide baseline information on the contaminant occurrence patterns of several classes of compounds within the Chesapeake Bay Watershed. Understanding the spatiotemporal dynamics of contaminants in surface water is the first step in investigating the effects of contaminant exposure on fisheries and aquatic environments.
Triazine herbicides and primary pelagic interactions in an estuarine summer situation
Journal of Experimental Marine Biology and Ecology, 1999
A cocktail of the s-triazines, simazine and atrazine, was introduced into three of four experimental tanks (volume 5 900 l) that contained a natural estuarine pelagic community from the Pomeranian Bight. Herbicide concentrations in the spiked tanks corresponded to about 10, 100 and 1000 times the background of the control with absolute values of each compound of 0.005 21 21 mg l (control) and around 0.04, 0.6 and 6 mg l (spiked tanks). Herbicide concentrations, as well as the response of phytoplankton and bacterial stock and turnover, were monitored over a period of 10 days. Both triazines remained at the initial levels in each system. In spite of high activity of both bacteria and microalgae, no herbicide-specific effect could be observed. This resistance is attributed to the inherent stability of a well established and balanced multi-species regenerating system. The low level of algae-herbicide interaction shows, however, that the coastal system under study has no degradative capacity with regard to those compounds. Riverine inputs will be transferred to the open Baltic with no major decontamination effects.