Sources, Bioavailability and Fate of Heavy Metals and Organic Contaminants in Compost Manure

This paper reviews the sources, bioavailability and fate of heavy metals and organic contaminants in compost manure and in soils of which the manure is applied. The toxicity of heavy metals and organic compounds in soil of which would have come from applied compost is also discussed. Type of materials, their background and where collected for use in composting contribute to the sources of heavy metals and organic compounds in compost manure. The materials that are major sources include sawdust, sewage sludge and municipal solid waste (MSW). Sewage sludge usually is collected from wastewater and or sewage treatment plants while sawdust is collected from timber industries that manufacture different items from raw wood. MSW is found at municipal operated landfills and dumping facilities. Both inorganic and organic contaminants are highest in sewage sludge because of enrichment that occurs during wastewater treatment process. Heavy metals such as iron (Fe), manganese (Mn), chromium (Cr), nickel (Ni), zinc (Zn) and copper (Cu) are found in sawdust and come from wood cutting metal component. The extent of heavy metals and organic compounds in sewage sludge depends on the type of wastewater being treated. Sewage sludge from industrial wastewater treatment plants has generally higher levels of heavy metals (copper, zinc, lead, iron, cobalt, nickel, chromium, cadmium) and organic compounds (polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins/furans and polyaromatic hydrocarbons) than that from household wastewater treatment plants. Electronic waste, metal (soft drink cans) and glass (food bottles) components in MSW are the major contributor to heavy metals. Source separation of the biodegradable waste from electronic waste, metal and glass components in MSW has been observed to reduce the level of Cu, Zn, Lead (Pb) and Fe in compost. Bioavailability and toxicity are influenced by factors such as type and amount of contaminant in the soil and compost, type of soil, amount of organic matter in the compost and other environmental conditions such as pH. _____________________________________________________________________________________________________________