State: atmospheric composition and climate

5.3.2 Persistent bioaccumulative toxic substances

Gaseous elemental Hg is a global pollutant with the highest concentrations in East, South and South-East Asia, and in the artisanal gold mining regions of Equatorial Africa and South America (see Figure 5.12) (UNEP and AMAP 2018).

Concentrations of POPs that are regulated and monitored under the Stockholm Convention have been reduced in Europe, North America, and Asia and the Pacific (UNEP 2014a; UNEP 2014b; UNEP 2015a; UNEP 2015b).

Measurements of regulated POPs in Arctic air and biota show predominantly downward trends for substances that have been banned for more than 20-30 years in developed countries, but the rate of their decrease has slowed (Hung et al. 2016). Trends of POPs in the Arctic appear to be sensitive to changes in climate, due to increased volatilization from sources (AMAP 2014, Ma et al. 2011) and to changes in Arctic land-use and emission patterns, such as increases in mining and shipping (UNEP and AMAP 2011) (see also Sections 4.3.2 and 4.3.3). Although Antarctica is the Earth’s continent least subject to direct human impact, low but sometimes significant contamination levels can be found there (Vecchiato et al. 2015). Concentrations of PAHs and PCBs in Antarctic snow have decreased over recent decades (Vecchiato et al. 2015).

Figure 5.12: Global distribution of annual mean gaseous elemental mercury concentration in near-surface air (top) and wet-deposition flux (bottom) in 2015 simulated by a model ensemble
Circles show values observed in ground-based monitoring. Source: UNEP and AMAP (2018).

Trends for many new PBTs, however, are not yet established, although baseline data have become available in some regions, such as Europe (UNEP 2015a). As some POPs have been regulated or banned, other unregulated PBTs have emerged as substitutes and are widely used in consumer and household items (e.g. furniture and electronics) and construction materials (Lee et al. 2016; Rauert et al. 2016). The growing number of listed POPs and candidate substances presents a resource pressure for existing monitoring programmes (UNEP 2015a). The emission, transport and environmental fate of new unregulated PBTs differs from regulated POPs, further challenging their assessment.