How do the various chemicals I.E Pesticides, Herbicides, etc used to manage GMO farms affect the surrounding soil it seeps into?

Expert response from holmquist1x

Friday, 11/05/2018 10:25

Believe it or not, I jump at opportunities to talk about aquatic life, so thank you for your interest. I developed a passion for aquatic animals early on and remain grateful that I have managed to explore my passions in ecotoxicology for over 25 years!

This discussion will focus on glyphosate and dicamba as examples of herbicides that are used to manage weed control on farms cultivating GM crops. As background, glyphosate binds strongly to soils limiting bioavailability and glyphosate rapidly degrades in a range of soil types and climatic conditions. Fifty percent dissipation times (DT₅₀), a measure of persistence, for glyphosate is typically less than one month and glyphosate does not build up in soil. Dicamba also degrades in a range of soil types and climatic conditions with 50 percent dissipation times typically of approximately 150 days and will not build up in soil.

The potential effects of glyphosate on soil macro- and micro-organisms has been extensively evaluated. Similarly, for soil microbes, functional endpoints such as carbon and nitrogen cycling in soil, have also been extensively evaluated. Glyphosate has been shown no long-term impact on these important biochemical processes. In addition, glyphosate has been shown to not impact growth, development and reproduction of important species of soil macro-organisms that are responsible for maintaining soil structure and functioning of these biotic communities. For example, glyphosate has been shown to not have short-term or long-term effects on earthworms or long-term effects to spring tails the most abundant soil macro-organism, and predatory mites (Giesy et al., 2000; von Mérey et al., 2016).

An in-depth assessment of glyphosate on soil biota has recently been published by von Mérey et al. (2016) and we point interested readers to this recent peer-reviewed paper for more information. In addition, an expanded discussion, specific to earthworms and glyphosate, was previously prepared for GMO answers.

Glyphosate promotes conservation tillage practices that lead to improved water and soil quality (Jordan et al., 1997; Haines and Uren 1990). Conservation tillage is a system of crop production where the farmer does little, if any, tillage. The system increases the residue from the crop that remains in the field after harvest through planting. By leaving crop residue undisturbed, microbial and other biological activity in the soil feeds on the stalks, leaves and other crop residues. The residue also reduces soil erosion, increases organic matter, improves soil tilth and, ultimately increases soil productivity. Farmers generally use herbicides like glyphosate and dicamba to kill weeds before planting to prepare conservation tillage fields for seeding.

Like glyphosate, dicamba also has been shown to not impact soil micro- and representative soil macro-organism communities (EFSA, 2011). Taken together, use of glyphosate and dicamba on GM crops is not predicted to have an adverse impact on soil biota, structure and function.

References:

• EFSA, 2011. Conclusion on the peer review of the pesticide risk assessment of the active substance dicamba. EFSA Journal, 9(1):1965.
• European Food Safety Authority (EFSA). 2015. Conclusion on the peer review of the pesticide risk assessment of the active substance glyphosate. European Food Safety Authority Journal 13:4302.
• European Food Safety Authority (EFSA). 2011. Conclusion on the peer review of the pesticide risk assessment of the active substance glyphosate. European Food Safety Authority Journal 9:165.
• Giesy JP, Dobson S, Solomon KR. 2000. Ecotoxicological risk assessment for Roundup® herbicide. Rev Environ Contam Toxicol. 167:35–120.
• Haines PJ, Uren NC. 1990. Effects on conservation tillage farming onsoil microbial biomass, organic matter and earthworm populations, in north-eastern Victoria.  Australian Journal of Experimental Agriculture 30: 365-371.
• Jordan D, Stecker JA, Cacnio-Hubbard VN, Li F, Cantzer CJ, Brown JR. 1997. Earthworm activity in no-tillage and conventional tillage systems in Missouri soils:  A preliminary study.  Soil Biology and Biochemistry 29(3/4): 489-491.
• Judson R, Houck K, Martin M, Richard AM, Knudsen TB, Shah I, Little S, Wambaugh J, Setzer RW, Kothiya P, Phuong J, Filer D, Smith D, Reif D, Rotroff D, Kleinstreuer N, Sipes N, Xia M, Huang R, Crofton K, Thomas RS. 2016. Analysis of the Effects of Cell Stress and Cytotoxicity on In Vitro Assay Activity Across a Diverse Chemical and Assay Space. Toxicol Sci. 153:409.
• Levine SL, von Mérey G, Minderhout T, Manson P, Sutton P. 2014. Aminomethylphosphonic acid has low chronic toxicity to Daphnia magna and Pimephales promelas. Environ Toxicol Chem. 34:1382-9.
• USEPA. 1993. Glyphosate: Registration Eligibility Document.
• USEPA. 2006.  Registration Eligibility Document for Dicamba and associated salts.
• von Mérey G, Mehrsheikh A, Manson P, Sutton P, Levine SL. 2016. Glyphosate and AMPA chronic risk assessment for soil biota. Environ Toxicol Chem. 35:2742-52.