The behaviour of 39 pesticides in surface waters as a function of scale

Abstract

Abstract:A portion of applied pesticides runs off agricultural fields and is transported through surface waters. In this study, the behaviour of 39 pesticides is examined as a function of scale across 14 orders of magnitude from the field to the ocean. Data on pesticide loads in streams from two US Geological Survey programs were combined with literature data from field and watershed studies. The annual load as percent of use (LAPU) was quantified for each of the fields and watersheds and was used as the normalization factor across watersheds and compounds. The in-stream losses of each pesticide were estimated for a model stream with a 15 day travel time (similar in characteristics to the upper Mississippi River). These estimated in-stream losses agreed well with the observed changes in apparent LAPU values as a function of watershed area. In general, herbicides applied to the soil surface had the greatest LAPU values and minimal in-stream losses. Soil-incorporated herbicides had smaller LAPU values and substantial in-stream losses. Insecticides generally had LAPU values similar to the incorporated herbicides, but had more variation in their in-stream losses. On the basis of the LAPU values of the 39 pesticides as a function of watershed area, a generalized conceptual model of the movement of pesticides from the field to the ocean is suggested. The importance of considering both field runoff and in-stream losses is discussed in relation to interpreting monitoring data and making regulatory decisions.

Watershed Vulnerability To Herbicide Transport in Northern Missouri and Southern Iowa Streams

“…Median herbicide losses were as follows: 3.9% for atrazine, 2.3% for cyanazine, 2.1% for metribuzin, 2.0% for metolachlor, 0.50% for acetochlor, and 0.33% for alachlor ( Figure 5). These median losses were 2.8-40 times higher than median herbicide losses reported by Capel et al (2) for 43 USGS National Water-Quality Assessment Program sites and for several hundred studies published in the international literature. These studies represented a variety of scales (e60 ha to >10 000 000 ha), soils, climates, tillage, and crops, making it the most comprehensive report to date on the topic of pesticide transport in surface runoff.…”

Effect of Scale on the Behavior of Atrazine in Surface Waters

“…The focus of this paper is on atrazine as an example of how a relatively conservative pesticide can behave. A companion paper (20) extends the understanding obtained from atrazine to other pesticides that are less conservative and/or less likely to be lost from agricultural fields in runoff.…”

“…Only small watersheds were used in this calculation to minimize a negative bias in the loads of atrazine due to its in-stream loss. Although in-stream losses generally will be minimal for atrazine, the in-stream losses could be substantial for other pesticides (20). The median small-scale LAPU value is equal to 0.66%.…”

“…This value can be considered a characteristic property of atrazine and be used as a basis to compare the extent of runoff of atrazine to the extent of runoff of other pesticides (20). Only small watersheds were used in this calculation to minimize a negative bias in the loads of atrazine due to its in-stream loss.…”

“…The variable influences on the extent of runoff caused by individual watershed characteristics and weather events are superimposed on the relatively invariant LAPU value. Capel et al (20) explores this hypothesis further for 38 other pesticides that were analyzed as part of the NASQAN and NAWQA programs.…”