A pesticide surface water mobility index and its relationship with concentrations in agricultural drainage watersheds

Abstract

An index to benchmark pesticide mobility relevant to surface water runoff and soil erosion (surface water mobility index, or SWMI) was derived based on two key environmental fate parameters: degradation half-life and organic carbon-normalized soil/water sorption coefficient (Koc). Values assigned with the index of each individual compound correlate well with the concentration trend of 13 pesticides monitored in six Lake Erie, USA, tributaries from 1983 to 1991. Regression using a power function of SWMI fits concentration data well at various percentiles in the database for each tributary and all six tributaries combined, with r2 ranging from 0.71 to 0.94 for the concentrations at the 95th percentile. Good agreement was also obtained between SWMI and the time-weighted annual mean concentrations (r2 = 0.67-0.87). Although concentrations at or near peaks tend to be driven by rare hydrological events (intense precipitation immediately after application), SWMI explains the peak concentration data generally well (r2 = 0.53-0.86). The SWMI-concentration relationship was further evaluated with two other pesticide monitoring databases: the U.S. Geological Survey National Water Quality Assessment Program White River Study Unit (1991-1996) at Hazelton, Indiana, USA, and the Syngenta (previously Novartis) Voluntary Monitoring Program with Community Water Systems at the Higginsville City Lake, Missouri, USA (1995-1997). The ability of the proposed SWMI to discriminate pesticide runoff mobility and its correlation with surface water monitoring data can be significant in the development of screening methodologies and data-based models for government agencies and/or practitioners in general facing increasing pressure to assess pesticide occurrence in aquatic environments.

Estimation of Upper Centile Concentrations Using Historical Atrazine Monitoring Data from Community Water Systems

“…Survey weights were calculated and associated with sampled measurements for the estimates of centile parameters and their variances. Th ese estimated aggregate centiles are diff erent quantities from siteyear or site-specifi c centiles, which have been the focus of other studies (Solomon et al, 1996;Chen et al, 2002;Larson et al, 2004). Th ese aggregate centiles may allow the estimation of an upper-bound value where sample sizes are insuffi cient for direct estimation of individual site-year centiles.…”

“…For example, if the fi rst three measurements at a given site-year are collected on 15, 17, and 23 January, then the associated weights for the fi rst two measurements are 15.5 and 4. Th is approach to calculating weights is similar to other approaches that have been used to estimate single-year percentiles for atrazine (Richards and Baker, 1993;Chen et al, 2002;Larson et al, 2004).…”

Estimating Catchment Vulnerability to Diffuse Herbicide Losses from Hydrograph Statistics

“…Th e diff erence in their sorption coeffi cients alone (factor of 2; Supplementary Table SI-5) does most likely not explain this order. Additionally, Gustafson et al (2004) and Chen et al (2002; acetochlor not included) successfully modeled the surface water concentrations in the Lake Erie tributaries by assuming smaller half-life values of acetochlor and alachlor than atrazine and metolachlor.…”

Use-Exposure Relationships of Pesticides for Aquatic Risk Assessment

“…Therefore, only the independent chemical properties of AERO and KOC were selected in this study for stochastic PRZM simulations. The two selected parameters were also used by other studies for estimating pesticide runoff potentials [21], [26], [27], [28].…”