processes.
Recent results indicate that a substantial amount of the mercury flux is in the methylmercury form which is highly toxic and bio-available. Currently, however, the present leaching of methylmercury forms only a small part of the actual amount stored in Swedish soils (the average methylmercury transport to the lakes per year is less than 0.2 per cent of the total methylmercury stored in soils see Figure 7.2). In addition, the soil stores are still increasing due to atmospheric deposition inputs and, unless the driving forces for the methylation and leaching processes are stopped (by reduced deposition of acidifying compounds - see Chapters 4 and 31), the soil will act as a supplier of mercury for a long time to come (Hultberg et al, 1994).
Figure 7.2 - Input/output balance of methylmercury (MeHg) in a coniferous forested catchment (1 km2) and the methylmercury mass balance of a 50 ha lake in southwest Sweden
Source: Hultberg et al, 1994