Transport and Fate of Agrochemicals in the Environment

Abstract

Synthetic agrochemicals applied at high concentration in the environment for pest control inevitably disperse from these sites, affecting non‐target species. As expected from the second law of thermodynamics, they will dilute spontaneously, transported into the available sinks in the environment by all transport mechanisms available. These dispersing chemicals comprise a diversity of manufactured products considered essential for modern economic civilisation, largely based on the consumption of fossil fuels. Despite the need for environmental protection, it is certain that the agrochemicals known as pesticides will continue to disperse into ecosystems given the greater needs for global food security that are expected to intensify. However, banning such chemicals because of real or perceived risks may not be a rational response. We now possess extensive information on the fate and transport of such agrochemicals. In this article, selected case studies using data generated in the past 20 years for a contrasting range of legacy and current chemicals (DDT, endosulfan, diuron and glyphosate) are used in illustration, suggesting operating principles that can be used for achieving rational environmental management using risk analysis. There is a clear need for all stakeholders including environmentalists, to take responsibility for monitoring agrochemicals, to better assess their risk and manage and minimise their consequences. The benefits from strong and rational stewardship, where manufacturers, regulators users and all those who benefit from their use promote rational management of these products needs clearer recognition by all. Such approaches based on risk management could largely obviate the less rational precautionary approach.

Research and practice: environmental action for improving water quality in cotton catchments since 1990

“…These data indicated that on an industry scale, the used of herbicides following the introduction for Roundup Ready had not changed significantly on average for all forms of cotton, largely because of greater use on conventional cotton (Crossan et al 2007;Kennedy et al 2011). These results were surprising, but consistent with the previous predictions regarding the selection of particular herbicides.…”

“…Monitoring of trash ginned from cotton during the 2002 season occurred over a 2-year period at three gin sites from different valleys (Crossan and Kennedy 2008 pesticide residues were detected in gin trash; 13 commonly used pesticides of cotton and DDE, the main aerobic breakdown product of DDT (Kennedy et al 2011). The concentrations of these residues were then characterised for risk of contaminating water using standard methodology (ECOFRAM 1992;Norton et al 1992) and the EPA guidelines (EPA 1999).…”

“…Figure 1 shows graphically contours of residual DDT, obtained by ELISA analysis of soil coupled with GIS (geographical information systems) (Shivaramaiah et al 2002). The presence of significant DDT residues remains at similar levels today (Weaver et al 2012); but because of the chemical properties of DDT and DDE (Kennedy et al 2011), their transport is limited and more than 90% of the DDT residues remain in the top 10 cm. Despite a half-life probably greater than 10 years in vertisols used for growing cotton, the extremely low solubility in water reduces aquatic risk (Kennedy et al 2011).…”

“…The presence of significant DDT residues remains at similar levels today (Weaver et al 2012); but because of the chemical properties of DDT and DDE (Kennedy et al 2011), their transport is limited and more than 90% of the DDT residues remain in the top 10 cm. Despite a half-life probably greater than 10 years in vertisols used for growing cotton, the extremely low solubility in water reduces aquatic risk (Kennedy et al 2011). Although some movement of DDE residues occurs down the soil profile to greater depth (Weaver et al 2012), this almost certainly represents transport on soil particles in these highly cracking soils and not leaching.…”

“…Although some movement of DDE residues occurs down the soil profile to greater depth (Weaver et al 2012), this almost certainly represents transport on soil particles in these highly cracking soils and not leaching. Because of the extremely low water solubility of DDT/DDE (Kennedy et al 2011), it is almost certain that residues do not represent a threat to livestock by contaminating ground water, despite their (Weaver et al 2012) suggestion. The real risk relates to soil biota that may consume soil organic matter, or their predators such as birds.…”