Ask Christen Farm Nursery: Pesticide Residue in Compost from Lawn Waste and Conventional Produce

The question: Should I be worried about residual pesticide levels in my compost I make myself or buy at Christen Farm Nursery?

In short: No, the residual levels are mostly broken down and the benefits of composting outweigh the risks of residuals in your garden.

The full answer:

A review of more than 100 studies on pesticide bio-degradation published in the journal Compost Science and Utilization states that in 2000 comparisons of pesticide concentration before and after composting shows that organochlorine compounds such as DDT (banned in 1972) was the most resistant to biodegradation. Pesticides in other categories decomposed moderately well to very well. Mineralization, or the decomposition of the chemical compounds in organic matter by which the nutrients are released in soluble inorganic forms that may be available to plants, on a whole accounted for a small portion of pesticide disappearance. Other fates include partial degradation to secondary compounds, absorption, humification (the break down and decomposition of organic materials), and volatilization (the solid or liquid state turns to a gas).

The research suggests that the degradation of pesticides in compost is similar to that in soil with some important distinctions. Composting can, but not always speed the degradation of the pesticides. The speed depends on a number of factors such as the nature of the pesticide, specific composting conditions and procedures, the microbes present and duration of the compost. All these affect the outcome of the pesticide degradation as all compounds have a life, half-life and quarter-life until they are completely degraded.

Therefore, it's important that you purchase compost that is properly processed for ultimate degrading or that you personally achieve the proper degrading with time, humates, heat, and adsorption. The 2000 study concluded that none of the composts analyzed in the cited studies exceeded concentrations thought to effect human health or be photo-toxic to sensitive plants.

The Takeaway: Making compost is the smart thing to do on several levels and it's most important to get the levels of nitrogen-rich "greens" and carbon-rich "browns" right than to worry that you added lawn clippings with residual pesticides in them or added food waste to your compost that wasn't USDA certified organic.