Mixed waste ‘compost’ & heavy metal contamination: Let’s stop living in a fool’s paradise


We all think household waste is relatively harmless and that rejects like plastic can be extracted out of the compost pile once the process is through. When I pored over some research papers, this is what emerged. To put it succinctly, what we throw enters the food chain, comes back and sits on our dining tables.

Household MSW contains wastes filled with heavy metals

These days, the nature of the products used by an average household not only in a developed nation but also a developing country like India, can contain various types of heavy metals. For example, batteries, bulbs and other various types of e-waste, many types of plastics, paints, inks, medicines, hospital waste, discarded medicines, body and beautycare products, household poisonous ‘solutions’ used for pest control, pesticides used for household gardens, etc. A waste stream of this nature can contain hazardous heavy metals like zinc, copper, nickel, cadmium, lead, chromium, mercury, etc. Compost generated from a mechanically segregated mixed waste tend to contain a greater amount of heavy metal concentration in the soil.

Why segregation is a must

Stephen R. Smith, Centre for Environmental Control and Waste Management, UK, says, “All types of municipal solid waste compost contain more heavy metals than the background concentrations present in soil and will increase their contents in amended soil… The metal contents of source-segregated MSW or greenwaste compost are smaller compared to mechanically sorted MSW-compost and sewage sludge…”

Since source-segregated and composted manure does not contain any of the above hazardous wastes, the “composts derived from source-segregated waste streams or greenwaste are generally reported to contain smaller amounts of heavy metals compared to mechanically-sorted products,” says Epstein et al, 1992.

Therefore, “… compost derived from these feedstocks is recognised as a potentially important source of heavy metals entering soil and the environment.”

Aerobic composting increases complexation of heavy metals

Image from Unsplash

As it is, aerobic composting—the method usually used for processing mechanically segregated MSW waste from the mixed waste lot—is said to increase “the complexation of heavy metals in organic waste residuals”. Composted residuals derived from MSW and greenwaste have a high affinity for binding heavy metals.

Adds Stephen Smith: “There is general consensus in the scientific literature that aerobic composting processes increase the complexation of heavy metals in organic waste residuals, and that metals are strongly bound to the compost matrix and organic matter, limiting their solubility and potential bioavailability in soil.”

According to him, “lead is the most strongly bound element and Ni the weakest, with Zn, Cu and Cd showing intermediate sorption characteristics.”

How this MSW ‘compost’ can pollute soil, human food chain and more

When loads and loads of MSW compost enters the soil, the long-term accumulation of heavy metals in the soil environment is a concern because “they potentially have important consequences for the quality of the human food chain, toxicity to plants and soil microbial processes…” adds Stephen Smith.

That’s mainly because these heavy metals tends to stay on in the soil for a very long time. And because of their very long residence times in soil, the heavy metals can wreak havoc on the soil, its produce and the end consumers of such produce. In other words, humans and animals.

Adverse effects of using such MSW compost for agriculture

  • Phytotoxicity, which is nothing but a toxic effect by a compound on plant growth, can severely reduce plant growth.
  • Human foodchain gets completely thrown off the track as there will be plant uptake of these heavy metals.
  • The heavy metals enter the human foodchain when food grown in such a soil environment is consumed.
  • It also enters the human foodchain via offal meat from animals ingesting compost treated soil.
  • Animal health will be put to risk when they graze in fields fed with this ‘compost’.

Any thinking individual will be unsettled by the hazardous effects that our household waste can have on our foodchain. But that’s not what usually happens. We all know why. That’s the reason why a majority of population loves to live in a state of delusive contentment thinking that Nature will somehow take care of everything.

If this is not a fool’s paradise, what is?

3 thoughts on “Mixed waste ‘compost’ & heavy metal contamination: Let’s stop living in a fool’s paradise

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