Marine pollution: emerging issues and challenges

With the rapid development of human society, there is an increasing diversity and geographic spread of substances being released into the marine environment. Above threshold values these substances can have negative effects on the biological component of these systems and are therefore classified as pollutants (Cabral et al. 2019). Pollutants can be introduced to marine environments directly through human activities, indirectly through runoff such as discharges of untreated or partially treated wastewater, and or by exchange with the atmosphere (Noone et al. 2013). The relative contribution of different pollutants from these pathways varies substantially between substances and also spatially and temporally (Bierman et al. 2011).Research on marine pollution is an important component of marine science, with the number of studies on this topic rapidly increasing through time (Figure 1a). Most of these studies have been conducted in shallow nearshore environments of sheltered estuaries and bays where human activities are concentrated (Halpern et al. 2008) whereas only very few studies have been conducted in open oceans and deep seas (Van Cauwenberghe et al. 2013, Cózar et al. 2014, Tournadre 2014. The research effort is not evenly distributed across the globe, with much of the published literature being produced in China, followed closely by the USA and various countries in Europe (Figure 1b). This reflects the substantial impacts of these nations on the marine environment (Halpern et al. 2019, Bhuyan et al. 2021 and their leading role in producing scientific outputs (Marginson 2021). Alarmingly, recent research on pollution in many developing regions such as Africa, Asia, and South America (Figure 1b), has demonstrated high levels of pharmaceuticals (Wilkinson et al. 2022). Hence, more research on marine pollution in these little-studied regions is necessary to gain a greater understanding of the spatial footprint of anthropogenic activities.