Large quantities of microplastic particles from cosmetics, clothing and industrial processes could be ending up on agricultural land that is fertilized with urban sewage sludge. This calls for urgent investigation if we are to safeguard food production and reuse wastewater products.

Unlike microplastics that pollute the oceans, little is known about the particles' prevalence and potential effects in terrestrial and freshwater environments. Because they are retained in sewage and domestic waste water after treatment in municipal plants (S. A. Carr et al. Water Res. 91, 174–182; 2016), they could be contaminating agricultural soils — with unknown consequences for farm ecosystems and food security.

We estimate from emissions data (see, for example, go.nature.com/2ce0z6l) that 63,000–430,000 and 44,000–300,000 tonnes of microplastics could be being added annually to farmlands in Europe and North America, respectively.

This figure exceeds the estimated global burden of microplastics in oceanic surface waters of 93,000–236,000 tonnes (E. van Sebille et al. Environ. Res. Lett. 10, 124006; 2015).