Lake Michigan Mass Balance

U.S. Environmental Protection Agency Great Lakes National Program Office (G-17J) 77 West Jackson Boulevard Chicago, IL 60604 EPA 905R-01-010 entire report (PDF 1.8Mb) Results of the Lake Michigan Mass Balance Study: Atrazine Data Report Prepared for: USEPA Great Lakes National Program Office 77 West Jackson Boulevard Chicago, IL 60604 Prepared by: Robert N. Brent, Ph.D. Judy Schofield, and Ken Miller DynCorp Science and Engineering Group 6101 Stevenson Avenue Alexandria, VA 22304 December 2001

Results of the Lake Michigan Mass Balance Study: Atrazine Data Report

December 2001

The U.S. Environmental Protection Agency’s Great Lakes National Program Office (GLNPO) and partners instituted the Lake Michigan Mass Balance (LMMB) Study to measure and model the concentrations of representative pollutants within important compartments of the Lake Michigan ecosystem. The goal of the LMMB Study was to develop a sound, scientific base of information to guide future toxic load reduction efforts at the Federal, State, Tribal, and local levels. Objectives of the study were to: 1) estimate pollutant loading rates, 2) establish a baseline to gauge future progress, 3) predict the benefits associated with load reductions, and 4) further understand ecosystem dynamics. The LMMB Study measured the concentrations of polychlorinated biphenyls (PCBs), trans-nonachlor, atrazine, and mercury in the atmosphere, tributaries, lake water, sediments, and food webs of Lake Michigan. This document summarizes the atrazine data collected as part of the LMMB Study, and is one in a series of data reports that documents the project. Future documents will present the results of mass balance modeling.

Atrazine is a triazine herbicide that is widely used in the U.S. to control broadleaf weeds in the production of corn and sorghum. Approximately 64 to 75 million pounds of atrazine are applied per year in the U.S., much of which is used in the “Corn Belt” region that includes the upper midwest surrounding Lake Michigan. Atrazine is generally applied to soil pre-planting or pre-emergence, but is sometimes also applied to the foliage post-emergence. Atrazine can enter surface waters, including Lake Michigan, through runoff, spray drift, discharge of contaminated groundwater to surface water, wet deposition (dissolution of atrazine vapor in rainfall and washout of particulate bound atrazine), dry deposition (dry settling of particulate bound atrazine), and sorption from the vapor phase. For human health protection, EPA has set a maximum contaminant level of 3 μg/L in drinking water. EPA also has set draft ambient aquatic life criteria at 350 μg/L for protection from acute effects and 12 μg/L for protection from chronic effects.

In the LMMB Study, atrazine and atrazine metabolites (deethyl-atrazine [DEA] and deisopropyl-atrazine [DIA]) were measured in atmospheric, tributary water column, and open- ake water column samples. From March 1994 through October 1995, over 1000 samples were collected and analyzed by gas chromatography/mass spectrometry. Atmospheric vapor, particulate, and precipitation samples were collected from eight stations surrounding Lake Michigan and three background stations outside the Lake Michigan basin. Tributary water column samples were collected from 11 tributary rivers that flow into Lake Michigan. Open-lake water column samples were collected from 35 sampling stations in Lake Michigan, 2 stations in Green Bay, and 1 station in Lake Huron. While sediment and biological tissue were sampled for mercury, PCBs, and trans-nonachlor, these compartments were not sampled for atrazine, because atrazine is relatively water soluble, degradable, and does not accumulate in these compartments.

Atrazine in Atmospheric Components

The predominant atmospheric source of atrazine, DEA, and DIA measured in this study was precipitation. In atmospheric samples, atrazine was seldom detected in the vapor phase. Only 3.7% of vapor phase samples were above sample-specificdetection limits that averaged 32 pg/m3 and 20.7 pg/m3 for samples analyzed at the Illinois Water Survey and Indiana University, respectively. Atrazine was more frequently detected in the particulate phase and in precipitation, with 23% and 50% of sample concentrations reported above sample-specific detection limits, respectively. The presence and concentration of atrazine in both the particulate phase and in precipitation was highly seasonal. Atrazine was generally not detectable in atmospheric samples during the fall and winter, but atmospheric concentrations peaked during the spring in connection with the agricultural application of the herbicide. Maximum monthly atrazine concentrations in the particulate phase ranged from 160 pg/m3 to 1400 pg/m3 among atmospheric sampling stations, and mean atrazine concentrations during the spring and summer (March 20 through September 23) ranged from 25 pg/m3 to 370 pg/m3 among atmospheric sampling stations. In precipitation, maximum monthly atrazine concentrations ranged from 100 ng/L to 2800 ng/L among atmospheric sampling stations, and monthly volume-weighted mean concentrations during the spring and summer ranged from 19 ng/L to 120 ng/L among atmospheric sampling stations. Concentrations of atrazine metabolites (DEA and DIA) were well correlated with atrazine concentrations and generally followed the same patterns.

In general, atrazine in the particulate phase was higher at atmospheric sampling stations surrounding the southern Lake Michigan basin than at those stations surrounding the northern basin. This is consistent with agricultural land use that decreases in intensity from south to north in the Lake Michigan region. Atrazine concentrations in precipitation were less reflective of local land use conditions and suggest longrange transport of the herbicide in addition to local inputs. Atrazine concentrations in precipitation were not consistently higher surrounding the southern Lake Michigan basin, and in fact, atrazine concentrations in precipitation were often higher at remote sampling stations in the far north than at stations surrounding the southern basin.

Lake Michigan Mass Balance Study Sampling Locations

Atrazine in Tributaries

Atrazine was detected above the method detection limit of 1.25 ng/L in 99% of tributary samples. Maximum atrazine concentrations in Lake Michigan tributaries ranged from 6.4 ng/L in the Manistique River to 2700 ng/L in the St. Joseph River, and mean atrazine concentrations ranged from 3.7 ng/L to 350 ng/L in these same two rivers, respectively. Concentrations of atrazine in tributaries were strongly influenced by geographical location and corn crop acreage. Mean atrazine concentrations in the Manistique, Pere Marquette, and Menominee Rivers were statistically lower than in the remaining eight measured tributaries except for the Muskegon River. The watersheds of these three tributaries are more forested and contain fewer agricultural influences than the other monitored tributaries. Atrazine concentrations were highest in the St. Joseph, Grand, and Kalamazoo Rivers, where agricultural influences were much stronger and atrazine use rates were 52 to over 160 lbs/mi2. For these three tributaries with the highest atrazine levels, distinct peaks in atrazine were observed in mid to late May, corresponding with the agricultural application of the herbicide. Distinct seasonal patterns of atrazine concentrations were not observed for the other tributaries. Concentrations of atrazine metabolites (DEA and DIA) in tributaries were well correlated with atrazine concentrations and generally followed the same patterns.

Atrazine in the Open-lake Water Column

Within Lake Michigan, atrazine concentrations in open-lake water column samples were relatively consistent. Average atrazine concentrations at open-lake sampling stations within Lake Michigan ranged from 33.0 to 48.0 ng/L. Atrazine concentrations within Lake Michigan were statistically greater than those measured at the reference station on Lake Huron and were statistically lower than concentrations measured at one Green Bay sampling station. Because the open lake was well-mixed with respect to atrazine, lake-wide averages could be calculated. Over the course of the study, lake-wide average atrazine concentrations increased from 37.0 ng/L in April/May 1994 to 39.7 ng/L in March/April 1995. During this same time period, DEA concentrations increased by 14.9% and DIA concentrations increased by 54.0%. While atrazine concentrations increased slightly during the study, open-lake average atrazine levels remained more than 50 times below the maximum contaminant level for drinking water and more than 300 times less than the proposed ambient water quality criterion for protection of aquatic life from chronic effects.  

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