Table 1.

Neurotoxins derived from the environment

Environmental toxin	Examples	Comments
Chemical toxins	Organic Polychlorinated biphenyls (PCBs) or Chlorinated hydrocarbons, TCDD (2, 3, 7, 8-tetrachlorodibenzo-p-dioxin), Fluorinated organic substances (per- and polyfluoroalkyl substances [PFAs] or perfluorinated compounds [PFCs])	Used in plastics and rubber products and pigments, dyes. They are persistent in aquatic ecosystems
	Inorganic compounds Heavy metals like arsenic, mercury, lead and cadmium Warfare agents like Sarin	Encephalopathies Peripheral neuropathies
Radiation	Sunlight, x-rays, radio waves, particle radiation, i.e., alpha and beta Particles and neutrons.	Predispose to cancer, congenital disabilities, or skin burns.
Pesticides	DDT Pyrethroids	Their poor bio-degradability results in bio- accumulation of chemicals and bio-magnification within a food web
Biological agents	Phytotoxins - derived from food plants and fruits	Phytotoxins e.g., Lathyrus sativus causing lathyrism,[3] Litchi fruit causes hypoglycaemic encephalopathy,[4] Cassava ingestion leads to cassavism due to cyanide toxicity,[5] Annona muricata associated with atypical parkinsonism.[6]
	Mycotoxins - derived as metabolite of fungi which act as neurotoxin for animals and human.	Ergot, fumonisin B1 and ochratoxin[7,8,9] have neurotoxic effects. Neurological manifestations can include encephalopathy, movement disorders like choreoathetosis, spasms and ballism,[10] epileptic encephalopathy[11]
	Algae toxins Cyanobacteria or blue-green algae bloom in higher temperatures in aquatic ecosystem which is associated with climate change.	They produce cyanotoxins which can result in neurotoxicity due to seafood poisoning e.g., paralytic shellfish poisoning (PSP), neurotoxic shellfish poisoning (NSP), and amnesic shellfish poisoning (ASP).[12]
Infectious diseases	Neurotropic viruses Bacteria e.g., Diphtheric toxin Protozoa e.g., malaria	West Nile encephalitis,[13] Zika virus[14] yellow fever,[15] dengue,[15] COVID-19.
Air pollutants	Carbon monoxide/Carbon di oxide	Most common and widely distributed air pollutant.
	Sulphur di oxide	Released from fossil fuels, domestic fires etc.
	Lead	Children and pregnant women are affected the most. Affects blood and brain in children.
	Ozone	Strongest oxidizing agent.
	Particulate matter	Complex mixture of organic and inorganic substances. Coarse particles with an aerodynamic diameter of 2.5 to 10 um (PM10), fine particles of less than 2.5 um (PM2.5) and ultrafine (UFPs) or nano-sized (NP) particles less than 0.1 um.