About Pyrethrins and Related Products

Pyrethrum/pyrethrins are botanical pesticides derived from the pyrethrum daisy (Chrysanthemum cinerariaefolium) and C. cineum). Pyrethrum refers to dried powdered flowers. Pyrethrin refers to any or all of the six forms of the biochemical pyrethrin that are responsible for the pesticidal activity. They make up about 0.1% of the dry weight of flowers. It is important to distinguish both of these from pyrethroids, which are synthetic molecules that resemble pyrethrins chemically but are more toxic and persistent in the environment. Products with pyrethroids are NOT permitted under the HRM by-law.

Powdered flowers are rarely used today. Most products contain pyrethrins that have been extracted from the flowers and concentrated by chemical processes. Because of their relatively low toxicity to humans compared to most synthetic pesticides, they are the most widely used pesticides sold for household and garden use. Pyrethrins are sold for example in aerosol sprays that are used around food areas, and as additives in insecticidal soaps and diatomaceous earth.

Their benefits, compared to most synthetic pesticides, e.g. diazinon and carbaryl (Sevin) are much lower toxicity to humans, and fast degradation in the soil. The latter is one of the major benefits of botanical pesticides compared to synthetic pesticides: because they come from natural products, they are generally readily broken down by soil organisms. Interestingly the synthetic pyrethroids persist much longer in the soil, even though chemically they belong to the same class of chemicals.

However, in spite of widespread use of pyrethrins in the home environment, pyrethrins are far from innocuous to humans and have been associated with life-threatening allergic responses, and have possible links with leukemia, amongst other possible adverse health effects. See PYRETHRINS/PYRETHRUM: Health Hazards

Pyrethrins disrupt insect nerve impulses, causing instant paralysis. Some insects can break it down so another natural product derived from sesame called PBO (piperonyl buyoxide) is often included; PBO inhibitis the enzymes that break down the pyrethrins. Pyrethrim/pyerthrins are broad spectrum pesticides, affecting natural enemies as much as pests and are extremely toxic to bees, fish, and other aquatic animals. See PIPERONYL BUTROXIDE: Health Hazards

Under all organic standards, PBO is a prohibited material. Pyrethrum or completely natural pyrethrins are given a RESTRICTED status by the CGSB/OMRI; which means that their use by an organic farmers requires the approval of the certifying bodies based on an assessment of need, alternatives, efficacy and ecological impact.

The SOUL standards for organic landscaping note that 'There are currently no pyrethrin products registered in Canada that do not contain synthetic contaminants.'