Deck 25: Agricultural Chemicals Pesticides and Fertilizers: Exposure and Impacts

Question 1

Ammonia is known as a mitochondrial toxicant which results in neurotoxicity in humans. How do other species' susceptibility indicate other actions of ammonia?

Answer 1

Ammonium ion does not pass the gill well, but ammonia gas does. It affects the base balance in fish and is generated in fish during exercise. The most sensitive species are diatom (plant/algae)>barnacle>fish and amphipod>shrimp.

Question 2

Which herbicides appear to be the most toxic to mammals? To plants?

Answer 2

The most toxic ones are those that are oxidation-reduction indicators or disrupt electron flow in photosystems. They readily generate radicals and are acutely toxic such as paraquat. Other more chronic toxicity depend on the halogenation and the presence of benzene rings. The ones more toxic to plants are those that target all plants, not just broadleaf plants. Until genetics allowed glyphosate metabolism/resistance in certain crops, this was a powerful defoliant. Clearly agent orange containing dibenzodioxin contamination as a result of the 2,4,5-T manufacture was a powerful military defoliant with human exposures cause chronic toxicity.

Question 3

Which insectides are mostly toxic to the insects and why? Which are toxic to insects and humans and may also affect bees?

Answer 3

The malathion or parathion pesticides required enzymatic activation to an oxon that was the toxic species. Mammals have enzymes that avoid this step by hydrolysis and convert the toxic oxon to a less toxic metabolite. Insects mainly have to go through the activation step, but this is problematic for bees. A compound this is toxic to all is nicotine. This compound from tobacco is toxic to humans, insects and bees. The neonicotinoids have recently been investigated due to severe apriary population declines that may at least in part be explained by the effects of neonicotinoids on bee behavior.

Question 4

Why are all fumigants toxic?

Question 5

Why can cholecalciferol (vitamin D₃) be used as rodenticide or warfarin?