Neonicotinoid insecticides or “neonics” — the most widely used class of insecticides worldwide — have long been linked to massive losses of bees and butterflies, despite industry efforts to downplay their leading role. Science also ties neonics to declining bird species, dramatic losses of fish populations, and birth defects in white-tailed deer.
But neonics may be a problem for more than just the birds and the bees. Commonly found in water supplies, food and human bodies across the country, these popular chemicals are increasingly becoming part of our daily lives. That’s also of increasing concern to health professionals as new studies illuminate the serious risks that these everyday exposures may pose for people, especially children.
While more research on neonics’ possible human health harms is sorely needed, what we already know is worrying, and scrutiny is growing. For example, California is currently considering whether to list some of the neonic pesticides under Proposition 65 based on their neurodevelopmental and reproductive effects (i.e., brain and sperm damage), with a committee of experts — the Developmental and Reproductive Toxicant Identification Committee — discussing it last month (see NRDC’s comments here).
However, since the evidence we have on neonics’ potential human health impacts to date is little known to the public, often ignored by regulators and (as with the wildlife data) downplayed by industry, it’s worth a quick review:
How neonics work: They target the brain and nervous system
Neonics are neurotoxic insecticides. They permanently bind to insect nerve cells, overstimulating and destroying them — commonly causing uncontrollable shaking or twitching, paralysis and (eventually) death. Neonics bind to nicotinic acetylcholine (nACh) receptors, so called because they are activated by nicotine. Neonicotinoids (meaning “new nicotine-like” substance) get their name because they activate nACh receptors too.
But nACh receptors aren’t only in insect nerve cells, they’re also in the brain cells of people, where they play a central role in the operations of our brain and nervous systems, including learning, memory, mood, sensory processing, and pain. And there’s reasons to fear the impacts of nicotine-like substances on the brain, particularly for young, developing brains. In fact, health experts have long warned pregnant women to avoid nicotine because we know it isn’t safe for the fetus.
To get even more fine-grained, neonics are designed to bind to a subunit of the nACh receptor, called the alpha-4-beta-2 (α4β2) subunit. This subunit is a part of all insect nACh receptors, but a lesser fraction of those in people. Nonetheless, critical areas of the human brain are densely populated with nACh receptors containing the α4β2 subunit, including: the cortex (responsible for planning, judgment, creativity, inhibition, attention, memory, language); the thalamus (emotion, memory, relay sensory information between the cortex and the cerebellum); and, the cerebellum (posture, balance, coordination, speech). In other words, this receptor subtype may number fewer in people than in insects proportionally, but it’s all over critically important areas of the brain.
To make an analogy, a needle poke will hurt an insect more than a human, but it is still important to ask what happens if a person gets that needle poke in a sensitive area like the eye. With neonics, the concern is about getting a needle poke (or many) in critical regions of the brain during sensitive life-stages of brain development.
Evidence of exposure: Half the U.S. population regularly dosed with neonics
To continue the metaphor, the first key question is how many people are getting poked with neonic needles? As it turns out, you don’t need to go looking in haystacks….