evidence: neurotoxin, substance that alters the structure or function of the nervous system. More than 1,000 chemicals are known to have neurotoxic effects in animals. The substances include a wide range of natural and human-made chemical compounds, from snake venom and pesticides to ethyl alcohol, heroin, and cocaine. [...] Neurotoxins are absorbed through inhalation, ingestion, skin contact, or injection and can have immediate or long-lasting impacts by causing neurons to malfunction or by disrupting interneuron communication. Slurred words or poor coordination due to toxic effects on neurons from alcohol consumption, for example, are temporary, whereas cognitive damage caused by lead exposure is irreversible. Certain neurotoxins are highly potent and have been developed into chemical weapons. The nerve agent sarin, for example, is an organophosphorous compound that is classified as a weapon of mass destruction; sarin gas can kill a person within 10 minutes of exposure. [...] In the modern era, there is significant concern about the combined effects of moderate and even low-level exposure to multiple neurotoxins; more research is needed, however, to determine the physiological significance of such exposures. In addition, thousands of other chemicals are suspected of having neurotoxic effects, though many remain untested.