CHEMICAL FOOTPRINTS [+]Enlarge Credit: Environ. Sci. Technol.

An ecological footprint is a popular metric that shows the amount of natural resources required to provide raw materials and food to sustain an individual or a country. Comparing the footprint to what nature actually can provide allows people to easily grasp their impact on the environment.

Environmental scientists have struggled to develop a similar footprint for chemical pollution that explains how the mix of chemicals released into the environment affects ecosystem health. Now, two separate groups report the first methods for calculating such an indicator for aquatic ecosystems. Analyses using these first-generation chemical footprints suggest that most European countries don’t have enough freshwater in their rivers and lakes to dilute chemical pollution to safe levels for ecosystems.

The large number of chemicals released into the environment and their different physical and toxicological properties have stymied previous attempts at developing a chemical footprint, says Michiel C. Zijp, an environmental scientist at the Netherlands’ National Institute for Public Health & the Environment and lead author of one of the studies. Some researchers have tried to summarize cumulative emissions of chemicals or their concentrations in the environment. “But what was missing was a comparison of environmental concentrations to levels that don’t cause damage to ecosystems,” says Anders Bjørn, an environmental engineer at the Technical University of Denmark and lead author of the other study.

Zijp and Bjørn independently came up with nearly identical frameworks for solving the problem. Both teams drew on chemical emissions inventories reported by the European Union. They then adapted a series of models to predict the toxicological impact that this soup of chemicals would have on plants and animals in the aquatic food web. To determine sustainable levels of pollution, the scientists turned to the EU Water Framework Directive, which states that some contamination is acceptable as long as no more than 5% of species experience low-level chronic effects. Finally, the two chemical footprint calculations determine how much water would be required to dilute the released chemicals to this safe level.

In Zijp’s study, he and his colleagues analyzed 630 organic compounds, such as benzene, formaldehyde, and tetrachloroethylene, emitted in the EU. Taking into account both fresh and marine water, the scientists estimate that the footprint of these compounds is smaller than the available water volume in Europe. But Zijp and his team found a different result when they generated a chemical footprint for pesticides in the watershed of the Rhine, Meuse, and Scheldt Rivers in northwestern Europe. In 2008, the pesticide footprint was about seven times greater than the available water in the rivers (Environ. Sci. Technol. 2014, DOI: 10.1021/es500629f). This was so even after the footprint shrank by nearly 80% since 1998, thanks to regulations curtailing the use of particularly harmful pesticides, Zijp says.

Bjørn and his team tested their chemical footprint approach on 28 European countries, examining the impact of 173 chemicals, including metals, solvents, and pesticides. When they compared the footprint to the amount of freshwater in rivers and lakes, most countries didn’t have enough water to dilute the chemical mixture to safe levels. For example, the Netherlands would need to multiply the volume of its rivers and lakes 18 times to dilute its existing chemical pollution (Environ. Sci. Technol. 2014, DOI: 10.1021/es503797d). Zinc and copper dominated the chemical footprints of all countries studied.

Both Zijp and Bjørn acknowledge that these chemical footprints need refining, and that the estimates are rough. For example, Bjørn thinks his team’s footprint would benefit from improved emissions inventories and updated models that take into account local environmental conditions such as how long chemicals stay in bodies of water.

But Zijp points out that scientists shouldn’t wait for perfect models because nations are already discussing how to manage pollution and could benefit from insights provided by the chemical footprint.