Release of organochlorine pollutants from forest fires: 2. possible long-term migration from ash and burnt soil.

The ash and burnt soil could release pollutants in a long term after forest fires, which poses health risks to ecosystems and human population. To date, our understanding of residues and release of organochlorine pollutants (OCPs) from ash and burnt soil after forest fires remains limited. In this study, a simulated fire via the burning of litter, grass, and humus was conducted in the Tibetan forest, while ashes and soil profiles after an actual fire event were sampled in half a year and three years after the fire. It was found that the ash-residue OCPs accounted up to 40 % of the total observed OCPs (both in ash and in air) after fire, and with the subsequent continuous release, the concentrations of OCPs in ash and burnt soil decreased more than one order of magnitude in the three years after the fire. The burning enhanced the migrations of OCPs on and in soil, and also pushed the redistribution of OCPs between soil organic matters and black carbon. Rainfall was considered as the key driving factor of OCP migration and re-partitioning, and dissolved organic carbon (DOC) might be the primary "carrier" of OCPs migration and redistribution. These results highlight the role of ash and burnt soil in the OCP releases, and under the situation of OCP reduction globally, the long-term sources of OCPs from forest fires cannot be ignored.