Anthropogenic contaminants are a growing concern. So far, more than 350,000 chemicals and mixtures of them have been registered for production and use, and numbers are increasing. As a result of their use, many of these chemicals find their way into freshwater systems and coastal waters.
The EU-project SOLUTIONS 1 has developed a method to determine to what extent the full range of man-made chemicals is likely to negatively affect the ecological status of surface water. As an indicator for the predicted environmental concentrations of these chemicals, a measurement known as the multi-substance potentially affected fraction of species (msPAF) is used, which ranges from 0 (no species affected) to 1 (all species affected). This indicator can be linked to the Sustainable Development Goal Indicator 6.3.2 "Proportion of bodies of water with good ambient water quality". Values below 0.05 (meaning less than five per cent of species are expected to be potentially affected) represent a low risk and can be seen as a good ambient water quality (shown on the maps below as green areas).
As part of the United Nations World Water Quality Assessment, and with co-funding from the United Nations Environment Programme, this method has been applied at a global scale, combining a high-resolution (1 km x 1 km) hydrological model (Wflow SBM: https://github.com/Deltares/Wflow.jl) with the modules on emissions (D-Emissions) and water quality (D-WaterQuality). The models are setup using the open-source package hydromt ( https://deltares.github.io/hydromt/latest/), which is developed under the umbrella of the BlueEarth Digital Environment ( https://blueearth.deltares.org/).
Calculating quality
A Baseline calculation for 2010 and two different scenarios for 2050 have been simulated for future projections. The socio-economic pathway SSP2 (a middle of the road pathway or business-as-usual world) is combined with the RCP6.0 scenario and a more extreme combination of SSP5 (high growth of income, fossil fuel-based) in combination with high global average radiative forcing values of the RCP8.5 scenario.
In the Baseline situation in 2010 on a global scale 91 per cent of water bodies show a "good quality" (msPAF < 0.05), although large differences can be seen between the various global regions: the lowest percentage of water bodies with "good quality" are shown in the highly industrialized areas of Asia (76 per cent), Europe (83 per cent) and North America (84 per cent).
Two combinations of climate (RCP) and socioeconomic scenarios (SSP) are calculated for 2050. On a global scale, the percentage of water bodies with "good quality" show a decrease of six per cent in the RCP6.0/SSP2 scenario and an even higher decrease of eight per cent in the more extreme RCP8.5/SSP5 scenario, as is shown in the figure below.
Comparing the scenario calculations for 2050 with the Baseline situation in 2010, we see (both for the "best case" and the "worst case" option) a decrease of water bodies with "good quality" and an increase of water bodies with a very high msPAF 0.8-1.0 in areas with toxic stress problems. We see both "hotspots getting hotter", "hotspots getting larger" and "more hotspots evolve" resulting in an overall increase of toxicity in these regions. See the figure below for some examples.
Freely available support
These problems seem to call for a proactive attitude and approach of both governments and people's initiatives to reduce the water-quality impacts of chemicals. These scenario analyses can help in developing strategies and evaluating the effectiveness of the mitigation options for the numerous pollutants.
The Toxic Stress results are available on a detailed geographical scale (1km x 1km), are free to download and use, and can be aggregated easily to large areas such as river basins or countries, making them suitable for many purposes for international organizations, governments, river basin commissions, consultants and other stakeholders.
More background information can be found in this document.
1 Van Gils et al, 2020