Role of low-latitude forests in modulating forest filter effect on a continental scale: Long-term simulation on PCB-153 in Chinese forests

Forests are important compartments influencing the environmental fate of persistent organic pollutants (POPs). To illustrate the effect of forests on the regional cycle of POPs, a level IV fugacity fate and transport model coupled with a detailed dynamic-forest module was applied to simulate the long-term variations of PCB-153 in China, where forest coverage accounts for approximately one fifth of land area. In the scenarios with forests, atmospheric outflow from China was 69% of that in the scenario without forests due to the enhanced storage in soil, degradation, and leaching. Previous studies regarded high-latitude areas, such as the polar region and boreal forests, as environments capable of reducing mobility of PCB-153, and they act as sinks of POPs. This modeling result suggests that tropical and subtropical forests may also play a similar role despite high temperatures favoring volatilization. Unlike boreal forest, the low-latitude forests may reduce the overall lifetime of PCB-153 in China due to enhanced degradation in warmer and moist soils of the tropical and subtropical area. Given that approximately half of the global forests are located in tropical and subtropical regions, they can be important environments influencing the global geochemical cycle and distribution of POPs, hence deserving more scientific attention by modeling and empirical studies.