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Daily News Blog

09
Nov

Liver and Kidney Damage Tied to Exposure to the Organophosate Insecticide Malathion

(Beyond Pesticides, November 9, 2018) A Tunisian study (published in January 2018) on the effects in pre-pubertal mice of exposure to malathion — an organophosphate pesticide first registered for use in the U.S. in 1956 — demonstrates significant distortion of liver and kidney biochemistry and function in the animals. Deleterious effects include compromise of feeding ability, metabolism performance, neurologic deficits, reduction of overall body weight, and simultaneous increases in the weights of livers and kidneys, with structural anomalies and lesions in those organ.

Organophosphates (OPs) have raised alarm bells for years. Some, such as chlorpyrifos and diazinon, have had their registrations cancelled for household uses because of the extreme health risks to children, but agricultural, golf course, and “public health” (mosquito control) uses remain commercially available and in use. Recently, Beyond Pesticides reported on research whose investigators support — and called publicly for — a worldwide ban on the compounds because of the serious health and environmental risks they pose, particularly for children.

Beyond Pesticides has written extensively on OP pesticides, including malathion and chlorpyrifos. Both are used widely in agriculture. Chlorpyrifos has been the subject of quite a ping-pong match in recent years: a scheduled ban by the Environmental Protection Agency (EPA), a rescinding of that directive, a court order to execute it, and now, a promise by the Trump administration to appeal that order. Malathion is used to control pests on a huge variety of food and commodity crops, by home gardeners, and in mosquito control efforts to limit mosquito-borne diseases. (Those programs typically involve aerial “adulticide” spraying to knock down adult mosquitoes in flight; it’s a strikingly ineffective approach to the problem.) Organophosphates are strongly linked to a number of human health risks, including neurological, reproductive, developmental, endocrine, and respiratory impacts, as well as liver and kidney damage.

Organophosphate pesticides were initially considered an improvement over organochlorine pesticides, such as DDT and dieldrin. Organochlorines (OCs) persist in the environment and can bioaccumulate, causing ongoing exposures and ecotoxicological impacts, whereas OPs degrade relatively quickly in the environment, thus reducing some of those organochlorine-associated risks. However, “though OPs are not as persistent as OCs, they are more acutely toxic and act to irreversibly inhibit . . . an enzyme critical to nerve function in both insects and humans.” That inhibitory impact inactivates acetylcholinesterase, an enzyme responsible for metabolism of the neurotransmitter acetylcholine. This is the “common mechanism of effect” for all OPs.

This inhibition causes the accumulation of acetylcholine, which can result in symptoms such as diarrhea, dizziness, headache, and muscle twitches, as well as potentially more-serious ones, including respiratory muscle paralysis, respiratory failure, coma, and death. The Turkish study cited below notes that, “Subjects exposed to organophosphates for [a] prolonged period might experience neuropsychiatric and mood changes, cognitive and memory deficits, polyneuropathy extrapyramidal symptoms,” or development of neurogenerative disorders (e.g., Parkinson’s disease, dementias). The liver and kidneys are considered among the main targets of malathion toxicity, which is mediated through oxidative stress — an imbalance, in cells, between the production of free radicals and reactive metabolites (so-called reactive oxygen species, or ROS), and their elimination by antioxidants. The Tunisian study identified those impacts as primary (see below).

Other studies have pointed to similar impacts and the oxidative stress mechanism. One such investigation, published in Ecotoxicology and Environmental Safety in October 2018, found hepatotoxic impacts of exposure to malathion in a fish species called rohu, a member of the carp family. Those included hepatic necrosis, fatty infiltration, congestion, and cellular swelling. The authors of that study concluded that their research “clearly revealed malathion as a potent hepatotoxic pesticide; therefore the injudicious, indiscriminate and extensive use of Malathion should be prohibited or at least reduced and strictly monitored.” An investigation by Turkish researchers, published in Toxicology Research in March 2018, also concludes that malathion increases oxidative stress, causes tissue damage, and decreases antioxidant status in rats. A third study, out of Egypt and published in April 2018 in the Asian Pacific Journal of Tropical Medicine, concluded that “compared to controls, malathion resulted in increased oxidative stress in [the] brain and liver.”

EPA’s determination of acetylcholinesterase inhibition as the “common mechanism of effect” is important. The Food Quality Protection Act requires that EPA calculate the multiple effects of pesticides with similar toxic properties; thus, cumulative risk assessment must consider, for example, malathion exposure plus any chlorpyrifos exposure, etc. EPA, not known for quick action on pesticide registration reviews, in 2016 issued, on the basis of a draft risk assessment, risk management recommendations for mosquito control professionals on the use of aerial malathion spraying. EPA was driven, no doubt, by concern related to increased spraying activity because of the then-rapid spread of the Zika virus, as well as other mosquito-borne illnesses. Information from the risk assessment was disturbing enough that the EPA took the uncharacteristic step; that information included evidence of histopathological lesions of the nasal cavity and larynx from exposures below the “dose” that typically causes the inactivation of acetylcholinesterase, as well as clinical signs of neurotoxicity (such as, tremors, salivation, urogenital staining, and decreased motor activity) in those exposed at levels 10 times those that cause such inactivation.

Beyond Pesticides advocates for transitioning away from toxic organophosphates for pest control. There are less- and non-toxic approaches to most pest problems that can drastically reduce the health and environmental risks associated with pesticide use. Learn more about organophosphates, pesticides generally, and shifting to organic agriculture through Beyond Pesticides’ Daily News Blog, journal Pesticides and You, Safer Choice pages, and its website pages on the transition to organic agriculture. 

All unattributed positions and opinions in this piece are those of Beyond Pesticides.

Primary source: https://www.epa.gov/mosquitocontrol/malathion

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