Because CCA leaches out of the treated timber over time there can be residues of arsenic, copper and chromium on the surfaces of the wood and it can be washed off by rain to accumulate in the soil or water below. All three metals pose a potential threat to the environment. According to the US EPA: ‘The amount and rate at which arsenic leaches, however, varies considerably depending on numerous factors, such as local climate, acidity of rain and soil, age of the wood product, and how much CCA was applied.’ (Office of Pesticide Programs 2002)