Are natural areas beginning to be as polluted as urban ones?

Soil contamination is one of the main threats to the health and sustainability of ecosystems. Green areas, including parks and gardens, constitute a fundamental part of our cities and are, on many occasions, the only contact that human beings have with nature.

An international study led by the Biodiversity and Ecosystem Functioning Laboratory (BioFunLab) of the Institute of Natural Resources and Agrobiology of Seville (IRNAS), of the Higher Council for Scientific Research (CSIC) in Spain, reveals that these areas are also highly subject to contamination of anthropic origin, from heavy metals to microplastics and pesticides. This contamination is potentially transferable to the natural ecosystems surrounding the cities; however, the differences in pollutant levels between soils in natural areas and urban green spaces have never been evaluated on a global scale.

The results obtained show that the soils of urban green spaces and adjacent natural areas share, in many cases, similar levels of multiple polluting agents (heavy metals, pesticides, microplastics and antibiotic resistance genes) in ecosystems around the world. .

“When we think of the forests and grasslands outside our cities, like the ones we usually go hiking, we think of relatively pristine places. However, in many cases, the natural areas that surround our cities are already as contaminated as our parks and gardens,” says Manuel Delgado Baquerizo, leader of the IRNAS BioFunLab and co-author of the new study. “This study constitutes a fundamental step in the investigation of pollution in our cities and natural areas, considering multiple sources of pollution simultaneously, and its objective has been to help us visualize the impact of human beings on the ecosystems that surround us” continues Delgado Baquerizo.

It is increasingly common to find garbage in natural areas, including relatively isolated beaches and the sea itself that bathes them. (Photo: NOAA)

Socioeconomic factors

Socioeconomic factors were essential to explain the presence of soil pollutants around the world. The regions with the highest GDP also show a higher level of heavy metals and the most populated cities show a higher proportion of microplastics. “Some of these contaminants such as microplastics, pesticides or heavy metals are even present in remote places like Antarctica,” says Asunción de los Ríos, a CSIC researcher at the National Museum of Natural Sciences (MNCN).

The study further indicates that increased levels of multiple soil contaminants are related to changes in the soil microbiome, including genes associated with resistance to environmental stress, nutrient cycling, and pathogenesis. “Our results highlight a negative association between the amount of pesticides and the microbial genes related to the cycling of phosphorus, one of the essential and most limiting nutrients of terrestrial ecosystems,” highlight Alexandra Rodríguez and Jorge Durán, scientists from the Biological Mission of Galicia (MGB), attached to the CSIC.

Taken together, the results of the new study show that human-induced soil pollution in natural areas close to urban areas mirrors that in urban green spaces around the world, and highlights that agents Soil contaminants can have dire consequences for the sustainability of ecosystems and human well-being. “A priori, it would be expected that soils in urban environments would be more likely to contain contaminants due to the fact that they are more impacted by human activity than their natural counterparts, but our results suggest that a dispersion is taking place towards the adjacent areas of the cities, which is worrying and suggests an urban footprint that is difficult to delimit”, indicates Eduardo Moreno, professor at the Autonomous University of Madrid and co-author of the study.

Twenty institutions from 17 countries have participated in this study, among which are the Center for Soil Science and Applied Biology of Segura (CEBAS) and the Institute of Agricultural Sciences (ICA), both from the CSIC, as well as various outside institutions. from Spain: the University of Zurich in Switzerland, the University of Sydney in Australia or the University of Pretoria in South Africa, among others.

The study is titled “Soil contamination in nearby natural areas mirrors that in urban greenspaces worldwide”. And it has been published in the academic journal Nature Communications. (Source: CSIC)