Heavy metals also occur naturally, but rarely at toxic level. Excess heavy metal accumulation in soil is toxic to human and other animals. Exposure to heavymetals are normally chronic (exposure over a longer period of time), due to food chain transfer.Acute (immediate) poisoning fromheavymetal is rare through ingestion or dermal contact, but is possible. Preventing heavy metal pollution is critical because cleaning contaminated soil is extremely expensive and difficult.Application of industrialwaste or sludge must abide by the regulatory limits set by the U.S. Environment Protective Agency (EPA).