Fertilisers and Pesticides Replace Fossil Fuels as Largest Source of Sulfur in Environment by Human Activity

At the beginning of the second half of the 20th century the world faced a new problem, that of acid rains. The reason was elimination of reactive sulfur to the atmosphere. The coal-power plants were historically the largest source of the reactive sulfur. However, quick and strict measures were taken to eradicate the problem and that brought success as well.

But anthropogenic sulfur release to the atmosphere is far from over and it comes through modification of the sulfur cycle. Now, a latest paper published in Nature Geoscience on August 10 has revealed fertilisers and pesticides used in croplands as the largest source of sulfur in the environment.

This further emphasises the need to monitor sulfur release and assess the possible negative impacts on the health of population residing in nearby agricultural areas. “Sulfur in agriculture is used in many different forms, and we haven't studied broadly how those different forms react in the soil. No one has looked comprehensively at the environmental and human health consequences of these [agricultural] additions," said Eve-Lyn Hinckley, lead author of the study.

Sulfur occurs naturally as an element and is a very important plant nutrient. It helps in the uptake of nitrogen. Sulfur is primarily extracted from fossil fuels, and pesticides and fertilisers are manufactured out of it. But, it has the innate ability to quickly undergo chemical transformation pertaining to its high reactive nature. The chemical transformation of sulfur can also lead it to react with heavy metals which poses a threat to the ecosystem, wildlife and also humans. 

According to the new findings of the research, sulfur in croplands poses a new challenge different from the acid rains. Commenting on it, Hinckley said, “This is a very different problem than the acid rain days. We've gone from widespread atmospheric deposition over remote forests to targeted additions of reactive sulfur to regional croplands. These amounts are much higher than what we saw at the peak of acid rain."

The presence of sulfur also opens up the study of possibilities of unknown risks. In the majority of researches that study the excess use of fertilisers and nutrients in agriculture, the focus remains on nitrogen and phosphorus. It is now widely known that these two elements can have detrimental effects on environment such as increased greenhouse gas emissions along with algal bloom that could be observed in downstream waters. As sulfur is used for long time in agriculture to improve the production and health of crops, the risks in increase of its amount in the soil are still not known widely. These activities also hamper the natural sulfur cycle.

One example is the accumulation of methyl mercury in the everglades of Florida. This, as per research from US Geological survey, is due to large use of sulfur on sugarcane in the everglades of Florida. Methyl mercury is a potent neurotoxin and it accumulates not only in the environment but also in the food chain. As we move upward in the food chain this toxin accumulates, meaning, it can affect each predator more than the prey that it consumed.

The researchers of the Nature Geoscience paper have also predicted that increase in sulfur will continue in many croplands of the world, for example India and China.