The Greening of Pesticide–Environment Interactions: Some Personal Observations

Abstract

Background: Pesticide–environment interactions are bidirectional. The environment alters pesticides by metabolism and photodegradation, and pesticides in turn change the environment through nontarget or secondary effects.Objectives: Approximately 900 currently used commercial pesticides of widely diverse structures act by nearly a hundred mechanisms to control insects, weeds, and fungi, usually with minimal disruption of nature’s equilibrium. Here I consider some aspects of the discovery, development, and use of ecofriendly or green pesticides (i.e., pesticides that are safe, effective, and biodegradable with minimal adverse secondary effects on the environment). Emphasis is given to research in my laboratory.Discussion: The need for understanding and improving pesticide–environment interactions began with production of the first major insecticide approximately 150 years ago: The arsenical poison Paris Green was green in color but definitely not ecofriendly. Development and use of other pesticides has led to a variety of problems. Topics considered here include the need for high purity [e.g., hexachlorocyclohexane and polychloroborane isomers and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T)], environmental degradation and the bioactivity of resulting photoproducts and metabolites, pesticide photochemistry (including the use of structural optimization, photostabilizers, and photosensitizers to achieve suitable persistence), the presence of multiple active ingredients in botanical insecticides, the need to consider compounds with common mechanisms of action, issues related to primary and secondary targets, and chemically induced or genetically modified changes in plant biochemistry. Many insecticides are bird, fish, and honeybee toxicants, whereas herbicides and fungicides pose fewer environmental problems.Conclusion: Six factors have contributed to the greening of pesticide–environment interactions: advances in pesticide chemistry and toxicology, banning of many chlorinated hydrocarbons, the development of new biochemical targets, increased reliance on genetically modified crops that reduce the amount and variety of pesticides applied, emphasis on biodegradability and environmental protection, and integrated pest- and pesticide-management systems.

Increased cancer burden among pesticide applicators and others due to pesticide exposure

“…69 Following absorption into the body, pesticides are often biotransformed to water-soluble metabolites for the purpose of detoxification and elimination. Rates of biotransformation can be rapid (hours to days), as in the case of OP insecticides, or extremely slow (years to decades), as is noted for OC insecticides, which accounts for the bioaccumulation of these lipophilic compounds in adipose tissue.…”

Chemical composition and larvicidal activity of essential oils from different Mentha L. and Pulegium species against Culex quinquefasciatus Say (Diptera: Culicidae)

“…The use of synthetic pesticides leads to many ecological problems. The most important negative impacts include ecological imbalance, high toxicity, residues in soil and water that affect human and animal health (Casida 2012;Roberts & Karr 2012), and the resistance of Culex against insecticides (Gordon & Ottea 2012). It was found that Culex populations could develop resistance on account of the widespread use of insecticides (Jones et al 2012).…”

Fifty Years Since Silent Spring

“…In the 1980s, based on mass, pesticide use declined somewhat because of the scaling back of pesticide overuse and the introduction of compounds that are used at lower concentrations (23). For example, the OP-chlorinated hydrocarbon chlorpyrifos, which was introduced in 1965, is typically applied in orange orchards at 2.9 kg active ingredient (a.i.)/ha.…”

“…In comparison, in the global north, mass of pesticide applied decreased from 1.8 kg a.i./ha to 1.6 kg a.i./ha, but the decrease is accounted for at least partly by substitution of materials that are toxic to the target organisms at lower concentration. However, many of the newer pesticides are also less toxic to nontarget organisms, although there are exceptions, such as with the toxicity of the neonicotinoid imidacloprid to honeybees and the toxicity of the herbicide paraquat (introduced in 1962) to mammals and birds (23). As a fungicide example, the older fungicide captan has a lethal dose to 50% of the population (LD 50 ) in fish of 0.034 to 0.3 ppm, whereas the newer strobilurin azoxystrobin has an LD 50 of 0.47 to 1.6 ppm (156), i.e., azoxystrobin has greater selective toxicity but remains a potential threat to aquatic environments, particularly because it has a half-life in soil of 70 days, in comparison to 1 day for captan (133,156).…”