Chapter 25
Estimated Ecological Effects of Atrazine Use
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on Surface Waters
Steven D. Mercurio Department of Biological Sciences, Mankato State University, Mankato,MN56002-8400 A model for ecological impacts of atrazine has been developed for surface waters in the Upper Midwest based on the seasonal intensive use of triazine herbicides utilizing the following parameters: 1) ecologically sensitive periods of stream ecosystems; 2) soil type and slope effects on atrazine runoff; 3) toxicity to various species in a flowing system; and 4) mitigation measures that are economically beneficial. Based on Southern Ontario data, stream concentrations of atrazine are inversely log-linearly related to soil water infiltration rates for soils with slopes 3 1-2 0-1 1-2 0-1 2-3
imperfect poor imperfect poor well-mod. well
2-3
well-mod. well rapidly
2-3
Depth To Water Table
Drainage Class
Dominant soil landscape (20); map scale = 1:1,000,000; map reliability: high to medium; subdominant soil landscapes and inclusions not considered for this table. ^Tentative correlation to U.S. soil classification system: Gleysolic - Aquic (i.e., wet) suborders; Gray Brown Luvisolic - Hapludalfs. Comparison to sites listed by Frank and Sirons (13) - Clay soils: AG-1, 3, 10,11; Loam soils: AG-4,5,6, 14; Sandy soils: AG-2,7,13. Site Ag-13 was described as sandy soil in the original reference. Variations in map scale and level of detail could result in different interpretations.
Map Symbol"
Table I: Soil Landscapes and Associated Soil Properties for 11 Southern Ontario Agricultural Watersheds (based on Frank and Sirons, 1979 (13)) Total Map Surface Texture Surface Slope Area, kha Class Soil Form (study area) Class (Parent Material) Development^ level 210.2 1-3% clay Gleysolic (clay) (5.1) level 1-3% 9.0 fine sandy loam Gleysolic (7.9) (silty clay loam) ridged 4-9% 126.1 silt loam Gray Brown (6.2) (silty clay loam) Luvisolic undulating 81.2 4-9% loam Gray Brown (loam) Luvisolic (1.9) rolling 4-9% 37.3 loam Gray Brown (3.0) (loam) Luvisolic undulating 1-3% 25.9 silt loam Gray Brown (5.5) (gravelly sand) Luvisolic undulating 1-3% 9.8 sandy loam Gray Brown (5.6) (sand) Luvisolic level 1-3% 236.5 silty clay Gleysolic (3.0) (heavy clay) undulating 4-9% 54.3 clay Gray Brown (2.4) (clay) Luvisolic level 210.2 1-3% clay Gleysolic (2.0) (clay) undulating 1-3% 15.0 sandy loam Gray Brown (4.5) (sand) Luvisolic
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328 mean atrazine concentrations reported by site (11 total) using SYSTAT Version 5.0 (SYSTAT, Inc., Evanston, IL). The data showed no significant correlation due to an important confounding variable, namely slope. If moderate slopes are present, as in sample AG-3, higher runoff concentrations would be expected. When moderate slopes were eliminated (4-9% slope range), a significant negative correlation between the mean of the annual time-weighted water concentrations (pg/L) and the logarithm of the infiltration rate expressed in cm/hr was observed (R =0.660, 7MX026, [mean atrazine concentration] = -1.22*log [infiltration rate] + 1.346]. These data indicate that as water infiltration decreased, stream atrazine concentrations increased. It also confirms the importance of moderate slopes on runoff, regardless of soil type (i.e. highest atrazine stream concentrations in the study were observed in an area of loam and clay soil textures and a moderate slope).
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2
a
Table II: Estimated Soil Properties from 11 Southern Ontario Sites Index Surface Infiltration Runoff Bulk density, Rate, Cm/hr mglm.3 Κ Class Site ^sat b
a
b
AG-1
1.3
low
high
7.6
AG-10
1.3
low
high
100 pg/L (29). However, egg hatchability of the caddisfly Triaenodes tardus Milne had an EC o of 22 pg/L (30), while chronic studies of leeches and snails led to an estimation of adverse effects to invertebrates at approximately 2% of the LC50S (31). Atrazine concentrations as low as 20 pg/L caused initial inhibitions of photosynthesis in phytoplankton, aquatic insect perturbations and other direct and/or secondary effects on the ecosystem (32-34). Atrazine concentrations in experimental pond mesocosm ecosystems ranging from 20-500 pg/L caused direct adverse effects on aquatic vegetation and gizzard shad and indirect influences on almost all species excepting macroinvertebrate total abundance (24). The lowest concentration causing direct effects of atrazine on higher aquatic species was reported for the carp, Cyprinus carpio. Following 6-12 hours of exposure to 10 pg/L atrazine, significant alterations in serum glucose and enzyme activity were noted (35). Additional information concerning the impact of atrazine on aquatic life and esturaine productivity is described by Stevenson (36) and Ward (37). Most of the toxic effects mentioned above for atrazine at concentrations
