More than 520 chemicals found in English soil, including long-banned medical substances

More than 520 chemicals have been found in English soils, including pharmaceutical products and toxins that were banned decades ago, because of the practice of spreading human waste to fertilise arable land.

Research by scientists at the University of Leeds, published as a preprint in the Journal of Hazardous Materials, found a worrying array of chemicals in English soils. Close to half (46.4%) of the pharmaceutical substances detected had not been reported in previous global monitoring campaigns.

The anticonvulsants lamotrigine and carbamazepine were among the human-use medicines reported for the first time in English soils.

A category of chemicals of particular concern to scientists are emerging contaminants, which are pharmaceuticals and other chemicals which have not been widely studied for their impacts on the environment or human health when they re-enter the food chain.

Water companies treat human faeces and remove some of the contaminants from wastewater at their treatment centres. The resulting product is treated biosolids, the organic matter from the human waste, and this is often disposed of by being spread on fields as fertiliser.

However, it appears that despite decontamination, hundreds of chemicals are leaching into the soil and in some cases staying there for many years. Several chemicals banned or withdrawn from use decades ago were found to persist in agricultural soils.

One of the researchers, Laura Carter, a professor of environmental chemistry at the University of Leeds, said: “Some of the chemicals were banned for use decades ago and their presence suggests that they are really persistent … so soils are a long-term sink of these pollutants.”

It is possible these chemicals will enter the food chain and be ingested by humans who eat food grown in these fields, she said. It could also harm farm productivity if the chemicals inhibit plant growth or negatively affect soil health.

“Some of the work which we did before this monitoring campaign was focused on the uptake and accumulation into crops and looking at effects on soil health and plant health,” she said. “What we need to understand is the subsequent pathway moving from the crops to consumption. Some of these contaminants can [affect] the soil health, and inhibit the nutrients taken up into crops.”

To conduct the research, Carter and her team asked farmers to send soil samples to their lab, and also visited some farms themselves. They took a variety of measures to detect what she calls a “chemical fingerprint” of the soil, using methods including mass spectrometry.

The EU is working to remove these emerging contaminants from wastewater across the continent by passing legislation requiring countries to implement “quaternary treatment”, which is an advanced pollution removal method that can get rid of micropollutants such as these chemicals. The UK has no plans to do this, and for now is sticking with the less precise tertiary treatment systems.

“Wastewater treatment processes can remove some contaminants,” Carter said. “We found that the processes are not as efficient as they need to be to remove them.

“These chemicals aren’t regulated for so there isn’t a drive to develop or to focus on technologies that can remove them. More advanced treatment like the EU’s planned quaternary treatment will typically remove more.”

Soil pollution is understudied compared with wastewater and river research, despite soil being so important for human and environmental health, and the fact contaminants can persist for decades.

“This is because of a combination of factors. There are analytical challenges, the chemicals are often at trace levels so you need to develop methods to extract them; the soil and the biosolids and the more agricultural focus means you have the complexity of the environmental metrics to contend with when you are trying to monitor them. And there is a lack of awareness about the pathways in which they enter the environment,” Carter said.

The contaminants can be removed, she said: “You can do processes such as actively planting crops so they take up the contaminants and that is a way of removing contaminants from the soil. But then you’d be left with trying to dispose of that contaminated plant.”

She was most surprised to find the banned chemicals, because this showed the long-term persistence of contaminants in soil. “They have been prohibited for use for quite some years so we were surprised by their persistence in the soils,” Carter said.

“We were also able to detect some anti-cancer drugs which was surprising because there isn’t very much research in this space so we haven’t seen those detected before.”

It is not the fault of farmers for spreading this, she said, as it is what they have been told to do in order to be sustainable.

“We need to regulate for them properly and we need education to make sure that everybody knows what is being applied and what the potential risks are that are associated with that,” Carter said.