Compost v soil: which is “clean”?

The oddest things breach MOE soil cleanup standards. Compost, for example.

Licensed compost makers operating with specific Ministry of the Environment approvals are permitted to sell “finished” compost for unrestricted agricultural use, as long as it meets the standards in the 2004 INTERIM GUIDELINES FOR THE PRODUCTION AND USE OF AEROBIC COMPOST IN ONTARIO. The 2009 Draft GUIDELINES FOR COMPOSTING FACILITIES AND COMPOST USE IN ONTARIO, uses the same criteria for finished AA compost, the only type that it proposes be sold without a warning, for unrestricted agricultural use.

It is therefore rather odd that finished  compost may breach the MOE’s own standards for agricultural soils for metals like arsenic, cadmium, chromium, lead and mercury, while lawful Table 2 agricultural soils may breach the compost standards for metals like copper, molybdenum, nickel and selenium. See the table below:

 Brownfield Soil Standards (O.Reg 153/04) vs. Aerobic compost standards.
Metals Table 1* (Background) for Agricultural soils Table 2** (health protective) standards for Agricultural soils Aerobic Compost Guidelines***
(mg/kg) (mg/kg) (mg/kg)
Arsenic 11 11 13
Cadmium 1 1 3
Chromium (total) 67 160 210
Cobalt 19 22 34
Copper 62 140 100
Lead 45 45 150
Mercury 0.16 0.25 0.8
Molybdenum 2 6.9 5
Nickel 37 130 62
Selenium 1.2 2.4 2
Zinc 290 340 500
*Table 1: Full depth background site condition standards.
** Table 2: Full depth site condition standards in a potable ground water condition.
*** 2004 interim guideline and the AA (uncontrolled) standard from the 2009 draft Compost Guideline

Does anyone know why?


  1. Gus Cheng

    An especially good question, Dianne. On the environmental consulting side of things, properties that would be otherwise, the current Table 2 standards cause us to label many sites "contaminated". My friend within MOE (who wishes to remain anonymous) says that these new criteria are scientifically based with consideration towards toxicity (for the knowledgeable, LD or LC 50s). If this is the case, why are compost standards so lax (comparatively speaking)? Typically, compost is used in garden beds and in some cases, vegetable beds. Is the MOE and MOH not concerned with food safety? To whom do we direct this question?

  2. I am guessing, but could the compost standards reflect the fact that the volume of compost additions to soil, even over extended periods, are a small fraction of the volume of the soils themselves. This could mean that the compost contaminants are substantially diluted and do not raise the soil background levels meaningfully. Just a thought.

  3. Maureen Reilly

    The Ministry of the Environment has been facilitating the diversion of industrial wastes into 'recycled' products — like compost. There has been a movement of sewage sludge and papermill sludges to 'soil conditioner' or 'fertilizer' products. The Ministry is in a conflict of interest. They are tasked with increasing diversion of wastes from landfill and also tasked with regulating waste in a way that is protective of the environment and public health.

    Increasingly what was 'waste' is becoming 'product' but without adequate regulatory safeguards to the public. The public has a huge interest in gardens and farmers markets these days. But with the government trend to allow more toxic soil ammendments we will see more toxins in food growing soil – more toxins in our food – and health problems from our body burden of industrial contaminants recycled into the food chain.

    Saxe Law has done a great job of pointing it out.

  4. Maureen Reilly

    The proposed compost regulation would allow cadmium, lead, mercury, arsenic elevation in home gardens and farmsoils from the distribution of compost. It looks like the Ministry of Health needs to play a stronger role by ensuring that soil standards in Ontario are protective of public health.

    Maureen Reilly

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