In the last post, I introduced the ways in which pesticides lead to soil pollution. You might be wondering, how serious is the issue? The answer is that it's complicated.
Around 0.1% of applied pesticides reach the target organism of the pest while the remaining percent contaminates the soil environment. The degree of contamination depends on the pesticide used. Some pesticide residues can even positively impact soils, by being an energy or carbon source for microorganisms, and can thus be assimilated or degraded in soil. However, studies have found negative effects on soil microorganisms and enzyme activities as well. Generally, it can be concluded that long-term application of pesticides has the potential to disturb the biochemical equilibrium in soils which can reduce soil fertility and productivity (Hussain et al., 2009). More research is required to understand molecular responses by soil microbes and enzyme processes to support risk assessments on pesticides before usage.
In reality, these assessments are not happening fast enough. As Prof Mengli discussed in Week 2, chemicals are being introduced into the environment without proper science-based risk assessments. This has had a severe impact on the global scale. A recent scientific analysis by the Stockholm Resilience Centre confirmed that the planetary boundary for chemical pollution has exceeded (Carrington, 2022). Contributing to this chemical pollution is the use of agrochemicals such as pesticides which leads to soil pollution. The nine planetary boundaries influence earth’s stability and so far, humanity has exceeded the safe operating space for four boundaries. This includes climate change, biosphere integrity, and biogeochemical flows of phosphorus and nitrogen.
Figure 1. Planetary boundaries, showing that the boundary for novel entities has exceeded the 'safe operating space'. Source: Stockholm Resilience Centre.
The study concluded that the boundary has transgressed due to the rate at which chemical pollutants are being introduced into the environment exceeding the capacity of policymakers to assess their risks significantly, let alone actions to curb potential problems they might cause. International solutions to mitigate harmful pesticide use, namely the Rotterdam Convention on the use and trade of hazardous chemicals, and the Stockholm Convention regarding the control and elimination of persistent organic pollutants (POPs) are significant steps forward. Although reductions in the trade of highly toxic pesticides have been recorded since the ratification of both treaties, challenges to phase them out still exist - which I hope to explore in subsequent posts.
References
Carrington, D. (2022, January 18). Chemical pollution has passed safe limit for humanity, say scientists. The Guardian. https://www.theguardian.com/environment/2022/jan/18/chemical-pollution-has-passed-safe-limit-for-humanity-say-scientists
FAO and UNEP. (2021). Global assessment of soil pollution: Report.
Hussain, S., Siddique, T., Saleem, M., Arshad, M., & Khalid, A. (2009). Chapter 5 Impact of Pesticides on Soil Microbial Diversity, Enzymes, and Biochemical Reactions. In Advances in Agronomy (Vol. 102, pp. 159–200). Academic Press. https://doi.org/10.1016/S0065-2113(09)01005-0