DDT’s Lingering Legacy
Lay summary by Rachel Shaffer
DDT is perhaps one of the most infamous chemical pesticides, but under the 2004 Stockholm Convention, it was banned for use in agriculture worldwide. However, new research reports that soil concentrations of the compound have not decreased as much as anticipated, suggesting potential additional routes of entry into the environment.
DDT is one of many “persistent organic pollutants,” or “POPs,” — compounds classified by their propensity for long-term accumulation in humans and the environment and their resistance to breakdown. Many of these compounds have been phased out through the Stockholm Convention, and their decreased presence in air and human monitoring suggested initial success of the global agreement. Yet, in depth soil monitoring has been incomplete.
In this study, the authors set out to collect all publically available soil measurements of DDT, along with its breakdown product (DDE) and two other common POPs (HCB and HCH). They compared the measurements of the chemicals by decade (1993–2002, and 2003–2012) and land type (agricultural or background). Next, using an established environmental fate and transport modeling system, they produced modeled concentrations for DDT and one isomer of HCH by decade and land type. By comparing the measured and modeled concentrations of the compounds, the authors aimed to evaluate the effectiveness of the Stockholm Convention.
Overall, the authors observed an important discrepancy between the measured and modeled data. While the models predicted a decrease in chemical concentration in soils between the first and second decade, the collected measurements demonstrated otherwise.
This work suggests that the previously established global agreement to phase out specific POPs may be less effective than anticipated. The contradiction between the measured and modeled concentrations indicates that there may be additional — and illegal — sources of the pollutants. Soil testing should continue in the future to better monitor contamination, and if concentrations remain high, additional global action may be warranted.
For further information
Read the Environmental Pollution original research article which this summary is based on Local organochlorine pesticide concentrations in soil put into a global perspective (September 2015).
Visit the profile of the research ambassador, Rachel Shaffer, who wrote this summary.
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