According to Danopoulos, there are two theories about how microplastics cause cell breakdown. The first theory is that their sharp edges break the cell wall and the second theory is that the chemicals in microplastics can damage the cell. The study showed that the probability of cell death was higher due to microplastics that had an irregular shape. “What we need to know now is how much microplastic stays in our bodies and what shape and size it is capable of crossing the cell barrier,” says Danopoulos.
Even without those answers, Danopoulos questions whether more care is needed to ensure that microplastics don’t end up in our food supply. “If we know that sewage sludge is contaminated with microplastics and that plants have the ability to absorb them from the soil, should we use it as fertilizer?” he says.
Banning the use of sewage sludge in agricultural lands
In the Netherlands, since 1995, the use of sludge on agricultural land has been banned. The country initially incinerated the sludge, but after problems arose at the plant in Amsterdam where the sludge was incinerated, it began exporting it to the UK. In Britain, sewage sludge was used as fertilizer on agricultural land.
Switzerland banned the use of sewage sludge as fertilizer in 2003 because “sewage sludge contains a wide range of harmful substances and pathogenic organisms produced by industry and households”.
Environmental officials in the US state of Maine also banned the practice in April 2022 after high levels of PFAS were found in farmland, crops and water. High levels of PFAS were also detected in the blood of farmers. Widespread contamination caused the closure of several farms. Under the new Maine law, mixing sludge with other organic materials is also prohibited.
A complete ban on the use of sewage sludge as fertilizer is not the best solution and could encourage farmers to use more nitrogen fertilizers, which are produced using natural gas, says Wilson of Cardiff University.
According to Wilson, using sewage sludge is an efficient way to use a byproduct instead of producing fertilizers that require fossil fuels. The organic matter in the sludge also helps return carbon to the soil, enriches it with nutrients such as phosphorus and nitrogen, and thus prevents soil degradation. “We need to measure the amount of microplastics in sewage sludge so we can determine where the concentrations are higher and start managing it,” says Wilson.
Wilson suggests that in places with high levels of microplastics, sewage sludge could be burned for energy instead of being used as fertilizer. One way to prevent farmland pollution is to separate the oils and fats that contain high levels of microplastics in wastewater treatment plants and use them as biofuel instead of mixing them with sludge.
Some European countries, such as Italy and Greece, bury sewage sludge in the ground, but in this case, there is a risk of microplastics entering the environment and contaminating water supplies and surrounding land.
Wilson and Danopoulos say more research is needed to determine the amount of microplastics in agricultural land and the effects they may have on the environment and human health. “Microplastics are on the verge of becoming a pollutant,” says Danopoulos. Pollution is something that is found where it should not be. Microplastics should not exist in water and soil. If we prove that they have negative effects, they will become pollutants and regulations should be established to control them.”
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