Hazardous Substances Thematic Assessment

 The QSR 2010 did not include any climate change issues in relation to hazardous substances. The Climate Change Thematic Assessment in this QSR places hazardous substances into the more general framework of climate change effects.

In general, temperature increases result in higher chemical reaction rates and could therefore lead to higher biological uptake, because of the higher growth rate in warmer waters and the higher reaction rates for contaminants. As a rule of thumb, an increase of 10˚C roughly doubles the reaction rates, so the expected temperature increase of around 2˚C would increase reaction rates by about 20%. Increased temperature alone has been shown to affect the volatilisation of pesticides and of POPs such as Dioxins, DDT, PCDD/Fs, PCBs and PAHs, but also degradation (e.g., hydrolysation of pesticides), thereby increasing global mobility and transportability (Kibria et al., 2021). The side effect of temperature rise is more rain, which leads to floods and higher run-offs of metals and POPs. Another side effect is the introduction of pest species in agricultural land, which can increase demand for pesticides in colder regions and thus increase their run-off to the marine environment. Finally, increased wind speeds and storms lead to the erosion of coastal landfill sites, the resuspension of coastal sediments and the erosion of coastline in general, releasing the hazardous substances they store into the marine environment.

Decreasing pH in seawater could lead to higher release of metals from sediment– since most metals are more soluble at lower pH– into the water phase and the biological community. The effects would probably not be great, given that most seawaters are above pH 7,5 and thus not inherently acidic. The pH change would most likely mainly be a problem in freshwater, where there is low buffer capacity.

For mercury, it has been suggested that the increasing temperatures, with related increasing hypoxia, forest fires and reduced ocean circulation, will increase methylmercury production in sediments, leading to higher releases from anoxic sediments to the overlying water columns. Forest fires increase the release of mercury stored in soils on land, and higher atmospheric residence time and winds increase the long-range transportation of mercury from tropical and subtropical regions to the Arctic regions (Krabbenhoft and Sunderland, 2013; Kibria et al., 2021).

The risks posed by climate change induced increases in pressures and contaminant concentration levels are reducing the effects of the efforts to reduce inputs, particularly that from the historic contaminants stored in sediments. These could be a contributing factor in inhibiting progress towards better status in the marine environment where the effects of hazardous substances are concerned.