On the influence of forests on the overall fate of semivolatile organic contaminants

Convincing experimental evidence exists that the presence of vegetation, especially forest canopies, enhances scavenging of semi-volatile organic chemicals (SVOCs) from the atmosphere and increases their depositional flux to the terrestrial surface relative to deposition to bare soil. Evidence from several modeling studies indicates that gaseous deposition to vegetation is the most efficient scavenging pathway, and, due to interactions between gas-particle partitioning in the atmosphere and resistance to diffusion through the cuticle of plants, that pathway is available for SVOCs with Log Koa between 7 and 11 and Log Kaw > -6. However, for enhanced scavenging by vegetation to influence the overall regional and global fate of SVOCs, it must represent a process that is competitive with the other fate and transport processes in the ecological system under consideration. The key question in evaluating the importance of the "Forest Filter Effect" on the regional and global fate of SVOCs is: Does scavenging from the atmosphere by vegetation have a significant influence on the inter-media partitioning, long-range transport and/or environmental persistence of SVOCs? Based on evidence presented below from the CoZMo-POP model and supported by results from other models that together represent our current state of knowledge, the Forest Filter Effect does not exert a controlling influence over regional or global contaminant fate and transport.