Herbicide-Induced Erosion Releases Banned Pesticides in Sediment

Washington, DC–(ENEWSPF)–November 11, 2014.  An international team of scientists has uncovered a new mechanism through which long-banned pesticides such as DDT may reemerge in our environment. Although a number of more recent studies have focused on the role that climate change is playing in the movement of older toxic chemicals, this study highlights the unknowns associated with pesticide use, showing the unexpected impacts that can occur when pesticide use patterns change.

Lac_de_Saint-André_et_vignoblesThe study, “Long-term relationships among pesticide applications, mobility, and soil erosion in a vineyard watershed,” published in the Proceedings of the National Academy of Sciences (PNAS), analyzed 100 years of sediment records collected from a lake near a French vineyard. Scientists were able to create a historical record of pesticide use in the region, and reconstruct erosion patterns seen over time. According to the study, the historical record lined up well with the restrictions and prohibitions on various pesticides that occurred over the years. That is, until the 1990s. Results show that increases in soil erosion line up with an influx of DDT into the lake. But the increase in soil erosion also lined up with the introduction and increase use of post-emergent herbicides such as glyphosate, the active ingredient in Roundup, in the 1990s.

“Analysis of changes in the rate of sediment influx into the lake between 1900 and 2011 suggested a link between soil erosion and patterns of herbicide treatment,” lead author Pierre Sabatier, PhD, of the Université de Savoie, France, told the news site environmentalresearchweb. “For example, glyphosate, used widely to curb grass growth between vine rows since the 1990s, was detected, through its metabolite, in a sediment sample over the last 20 years. Further, this herbicide-induced erosion has re-mobilized DDT and its metabolites – banned in 1972 but lingering in the vineyard soil – into the lake.”

The researchers reasoned that erosion was occurring because of the permanently bare soil conditions created by frequent herbicide spraying. “The soils underwent a change in storage conditions, converting from sinks to sources of pesticides,” the study asserts.

The discovery of this new externality associated with conventional farming strengthens calls from proponents of organic agriculture to replace toxic chemicals with practices that work with nature and build natural pest resiliency from the soil up. Included within the Organic Foods Production Act is the requirement that organic farming systems “contain provisions designed to foster soil fertility, primarily through the management of the organic content of the soil through proper tillage, crop rotation, and manuring.” Previous studies have shown that instituting organic practices does create healthier soils than conventional techniques. A paper published in 2010 found that organic strawberry farming resulted in both healthier soils and higher quality fruit. Research from the U.S. Department of Agriculture’s Agricultural Research Service determined that organic farming builds soil organic matter better than no-till conventional techniques that rely on chemical herbicide inputs.

As organic agriculture continues to grow, it is important that consumers become active in defending the integrity of organic production, so that harmful practices which undermine healthy soil are never instituted. Take action for strong organic standards by visiting Beyond Pesticides Save Our Organic program page. And learn more about the importance of organic agriculture through our program page.

Sources: PNAS, environmentalresearchweb.org, http://www.beyondpesticides.org