Green Chemistry: Pesticides

Green chemistry (see other articles on this site for an application of its principles) continues to be a major research topic for chemical industry. The need to quickly and easily generate compounds of chemical interest while minimizing toxicity and the generation of undesired byproducts is quickly becoming a driving force for chemical companies to pursue such avenues. Likewise, the control of pests continues to be at the forefront of agricultural development efforts, as pests cause untold millions of dollars of damage to crops every year. Pests are ever adaptive, quickly developing resistance to most insecticides; the very strongest of the insecticides invariably cause illness among farm workers who are exposed.

A latest innovation from Dow is spinosad, which is a highly selective - and most importantly - environmentally friendly insecticide. Produced by a soil bacterium, it controls many of the insect pests found in typical cash crops. Unlike traditional chemical pesticides, it does not persist in the environment - one of the hallmarks of "green chemistry".

The controlling of insect pests is paramount to maintaining the high level of farm productivity our culture currently enjoys. How was spinosad developed? Fermentation broths were isolated in agricultural experiments and produced numerous leads. One promising candidate was the extract of a Caribbean soil sample. It was found to be active on mosquito larvae. The microorganismin question, Saccharopolyspora spinosa, was subsequently isolated from the soil sample. Spinosyns are unique macrocyclic lactones (a type of organic molecule containing a tetracyclic core with two sugar groups attached). These material has been included in commercial products such as Tracer® Naturalyte® Insect Control and Precise®, acting as the active ingredient.

When Insects are exposed to spinosad, they exhibit symptoms of neurotoxicity: lack of coordination, tremors, and involuntary muscle contractions leading to paralysis and death. Although the mode of action of spinosad is not fully understood, it appears to affect receptors in the insects nervous system.

Spinosad is just about the perfect "green" pesticide. It doesn't leach into ground water, volatilize into the air, or persist in the environment. It slowly degrades when exposed to light. It's virtually nontoxic to mammals and birds. Although the chemical *is* moderately toxic to fish, it's less toxic than many other insecticides that are currently in use.

All of these properties combined make spinosad a promising up-and-coming "green" pesticide.