I recently read about the fascinating urban death project (linked to the project website) which converts deceased humans into crop compost to reduce burial costs, solve the problem of overcrowded cemeteries, and protect the environment by recycling.
The process works as follows: the body is buried with carbon-rich materials (some of which include sawdust, dry leaves, straw, and paper) under more than 60oC for a few months during which it is composted by microbial decomposition. All pathogens including bacteria and viruses in the body are expected to be killed. I must admit I was surprised by people’s reactions to this; in fact, some people saw this as showing a lack of respect for the just to save money or protect the environment. But, for me what is truly interesting, as a former scientist, is the problem of heavy metals from the decomposing bodies.
When we talk about the presence of heavy metals in our body, we may not realize that many heavy metals could have accumulated in our hair, nails, bones and organs from years of exposure to contaminated air, food, and water. These toxic heavy metals--including arsenic, cadmium, mercury, and lead--become concentrated in the body and are left in the compost after the decomposition process. (Do read my previous post, titled, Top Four Toxic Metals in Water: Facts and Testing, to learn more about their toxicity.)
Heavy metal contamination is indeed a big concern in compost because the metals could leach into the soil and groundwater, risking our health.
Sources of Compost
Typical sources of compost are recycled waste, human waste from sewage sludge, and animal manure. Recycled waste is a good source of compost material as 20-30% of what we throw away can be composted rather than buried in a landfill. Household and commercial food scraps, soiled paper, grass clippings, plants, and branches are often recycled by programs, such as Recology SF (link to the organization’s compost website).
Bio-plastics labeled as compostable can be sorted from residential and commercial waste and collected for composting purposes. Check out the Z-best composting facility in Gilroy in California (link to the World Centric presentation) for more information on waste recycling and composting from recycled waste.
Human waste is another viable source after it has been treated at a wastewater treatment plant (link to the Wikipedia for wastewater treatment). The sludge from the sewage treatment plant contains rich nitrogen and phosphorus, but also harmful pathogens, such as bacteria and viruses, which must be removed. The resulting sewage sludge, often called biosolids, can be used as compost after meeting the appropriate regulatory standards.
Animal manure or waste (downloadable PDF for animal manure composting) from animals such as cattle, horses, dogs and cats can also be collected for composting.
Regulation of Heavy Metals in Compost
The U.S. EPA regulates biosolids as compost and the organization sets pollutant limits. The local government can decide if biosolids will be used in fertilizers, incinerated, or deposited in a landfill. If biosolids are used in fertilizers, each state regulates operations and permits and pollutant limits.
The EPA regulates biosolids under title 40 CFR 503 (link to chapter 1 of the EPA guide to part 503 rule). CFR 503 Title 40 regulates the concentration of heavy metals (link to the 40 CFR 503.13-pollutant limits) including arsenic, cadmium, copper, lead, mercury, molybdenum (has been removed recently from the list), nickel, selenium, and zinc. These metals are quantified under four different categories: ceiling concentrations, pollutant concentrations, cumulative pollutant loading rate, and annual pollutant loading rate.
State regulations are more stringent than the federal for heavy metals in compost. California composting regulations (link to regulatory requirement), for instance, are more stringent on the concentrations of pollutants for the above-listed heavy metals, some at only half or less the concentration compared to the federal level. As chromium is of particular concern in land and groundwater in California, the state requires that it be monitored in addition to the metals outlined in CFR 503.
Heavy Metal Analysis in Compost
Depending on the sources of the different composts, analytical methods for heavy metals differ.