EPA Science Inventory

MEASURED CONCENTRATIONS OF HERBICIDES AND MODEL PREDICTIONS OF ATRAZINE FATE IN THE PATUXENT RIVER ESTUARY

Citation:

McConnell, L., J. A. HarmanFetcho, AND J. Hagy, J.D., III. MEASURED CONCENTRATIONS OF HERBICIDES AND MODEL PREDICTIONS OF ATRAZINE FATE IN THE PATUXENT RIVER ESTUARY. JOURNAL OF ENVIRONMENTAL QUALITY 33:594-604, (2004).

Description:

McConnell, Laura L., Jennifer A. Harman-Fetcho and James D. Hagy, III. 2004. Measured Concentrations of Herbicides and Model Predictions of Atrazine Fate in the Patuxent River Estuary. J. Environ. Qual. 33(2):594-604. (ERL,GB X1051).

The environmental fate of herbicides in estuaries is poorly understood. Estuarine physical transport processes and the episodic nature of herbicide release into surface waters complicate interpretation of water concentration measurements and allocation of sources. Water concentrations of herbicides and two triazine degradation products (CIAT)(6-amino-2-chloro-4-isopropylamino-s-triazine and (CEAT) 6-amino-2-chloro-4-ethylamino-s-trazine, were measured in surface water from four sites on forty days from 4 Apr. through 29 July 1996 in the Patuxent River estuary, part of the Chesapeake Bay system. Atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) was most persistent and present in the highest concentrations (maximum = 1.29 ?g/L). Metoachlor (2-chloro-6'-ethyl-N-(2-methoxy-1-methyl-ethyl)-o-acetoluidide), CIAT, CEAT, and simazine (1-chloro-3,5-bi-sethylamino-2,4,6-triazine) were frequently detected with maximum concentration values of .61, 1.1, 0.76, and 0.49 ?g/L, respectively. A physical transport model was used to interpret atrazine concentrations in the context of estuarine water transport, giving estimates of in situ degradation rates and total transport. The estimated half-life of atrazine in the turbid, shallow upper estuary was t1/2=20 d, but was much longer (t1/2 =100 d) in the deeper lower estuary. Although most (93%) atrazine entered the estuary upstream via the river, simulations suggested additional inputs directly to the lower estuary. The total atrazine load to the estuary from 5 April to 15 July was 71 kg with 48% loss by degradation and 31% exported to the Chesapeake Bay. Atrazine persistence in the estuary is directly related to river flows into the estuary. Low flows will increase atrazine residence time in the upper estuary and increase degradation losses.

Purpose/Objective:

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Record Details:

Record Type: DOCUMENT (JOURNAL/PEER REVIEWED JOURNAL)
Start Date: 03/20/2004
Completion Date: 03/20/2004
Record Last Revised: 03/25/2013
Record Created: 03/18/2004
Record Released: 03/18/2004
OMB Category: Other
Record ID: 80124

Organization:

U.S. ENVIRONMENTAL PROTECTION AGENCY

OFFICE OF RESEARCH AND DEVELOPMENT

NATIONAL HEALTH AND ENVIRONMENTAL EFFECTS RESEARCH LAB

GULF ECOLOGY DIVISION

ECOSYSTEM DYNAMICS AND EFFECTS BRANCH