Pesticides remain a ongoing source of troubling headlines. Recent findings reveal the emergence of up to 24 new toxic by-products formed as pesticides break down, substances that have not been tracked until now and whose harmful effects can surpass those of the original chemicals. These transformation products are created through natural chemical reactions once pesticides are applied, and many have spread beyond the fields into broader environments. These insights come from a collaborative effort among researchers and institutions dedicated to safeguarding water and soil quality.
A study conducted by the Institute for Environmental Diagnostics and Water Studies at CSIC, part of the Supreme Council for Scientific Research, in partnership with the Swedish University of Agricultural Sciences, identified 24 waterborne degradation products. The work shows that these compounds can be generated from pesticides that have never before been detected in the environment, highlighting a gap in monitoring as regulations focus mainly on the original substances. The research underscores that these by-products can form and accumulate long after the pesticides are applied, raising questions about their persistence and distribution in nature.
The findings were published in Environmental Science and Technology, and they illuminate how frequently these transformation products appear in environmental samples despite stringent controls on pesticide use in agriculture. The study notes that some by-products may exhibit toxic effects that exceed those of the pesticides from which they originate, presenting a potential shift in risk assessment for agricultural chemicals. This points to the need for broader surveillance that includes degradation products alongside parent compounds.
These conversion products are the substances created when pesticides break down through environmental processes, including interactions with light, water, and soil minerals that drive chemical changes after application.
The researchers warn that the amounts of these substances detected in the environment could pose an environmental risk due to their heightened dispersion and mobility. They can travel through soils and reach aquifers from which drinking water is drawn. Because their presence is not routinely monitored, these compounds may pose a hidden risk to human health. This concern is voiced by project coordinator Pablo Gago Ferrero, a researcher at the IDAEA-CSIC who leads the study.
The team employed a novel approach to identify these degradation products in Sweden, combining advanced analytical chemistry with a systematic review of regional pesticide distribution. This dual method allowed the researchers to spot new by-products even at very low environmental concentrations and to map how widely they might spread across ecosystems.
The findings indicate that many by-products appeared at higher concentrations than the original pesticides at the moment of formation, and some carried predicted toxicities greater than those of their parent compounds. Even with strong environmental controls, harmful substances are still being released and dispersed in the environment, underscoring the need for vigilance and expanded monitoring.
In some cases the parent pesticide cannot be detected in soil samples, which can give a false impression that there is no issue. Yet the transformation products continue to exist and may pose risks that are not immediately apparent. The study revealed that many of these by-products have not been cataloged in common databases. Consequently, efforts to identify them were enhanced and their records added to the PubChem repository, which should streamline future recognition and assessment of these substances.
Several of the newly identified substances have already been incorporated into Scandinavian monitoring systems, highlighting the value of including degradation products in regulatory programs. The authors suggest that similar expansions are necessary elsewhere, especially in countries with intensive agricultural activity such as Spain, to understand which by-products form and what health and environmental risks they may pose. Strengthened surveillance will help ensure that risk controls cover both original pesticides and their transformation products.
Reference article: DOI: 10.1021/acs.est.1c00466
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