Why Do Some Toxins Persist Despite Chemical Reactions?

[syfry]

Logic tells me that any substance or material can harm (or benefit) life only by reacting.

And once reacted, a molecule should form, and that should continue to happen in a variety of ways until at some point they should arrive at a molecular combo whose bonds are strong enough that at regular temperatures around Earth, the molecules are stable enough that they won't be harmful even if any of their individual atoms might still harm life (if they escape the bond).

But things like mercury, lead, and forever chemicals seem to be persistent. So why is that?

Are their strongest bonds still relatively weak enough that their molecules will swap their atoms for the cellular atoms in biology?

What's the explanation?

 

[Baluncore]

A catalyst is not consumed by the reaction.

A prion copies itself and lives on.
https://en.wikipedia.org/wiki/Prion

 

[sophiecentaur]

The term "toxin" covers a range of effects and timescales so you'd really have to pick some more specific examples and address each one individually and in the context of the organism it affects.

The effect of toxins on our bodies is a legacy of our evolutionary past. For instance, our kidneys do not deal well with heavy metals so we can get lead poisoning. That can be attributed to the fact that lead is not around in sufficient quantities to affect significantly our ability to reproduce so why would evolution throw up. an ability to deal with it? 'Nature' is as lazy as it can get away with - a bit like politicians running a country.

 

[syfry]

Lead is a good example. It's in a lot of soil so fairly widespread (but perhaps not enough to cause evolutionary pressures... although has any life evolved to withstand lead?).

The evolutionary side is interesting but for this question I'm more curious about why the effects of lead don't become 'tied up' by molecular combos that make the lead more inert or inactive (at least temporarily until sufficient temperatures would free its molecular bonds).

Baluncore brought up a good point about how catalysts don't get used up by the reactions they enable.

But is lead a catalyst, in the case of its harmful reactions with our bodies? (or with the bodies of other animals?)

Are most of forever chemicals in reality catalysts? (specifically in the cases of their harmful effects to life)

 

[sophiecentaur]

I don’t think you can be selective when looking for a causal relationship here. You can’t eliminate evolution in any explanation or description of our biology. Evolution does what it does (but it's just a catch-all term). If the energy taken to adapt is too high then organisms just put up with risk and sometimes die out. It would be very surprising to find no extremophiles that use lead compounds as a source of energy. Remember, bacteria have always ruled the world. We are just a blip in time.

 

[Baluncore]

Remember, bacteria have always ruled the world. We are just a blip in time.

A circular chromosome of bacterial DNA, is a persistent self-replicating chemical, that just goes rolling on, for hundreds of millions of years.

 

[Baluncore]

But is lead a catalyst, in the case of its harmful reactions with our bodies? (or with the bodies of other animals?)

No, not as a catalyst.
https://en.wikipedia.org/wiki/Lead_poisoning#Toxicodynamics

Lead is a biological problem when it is in an organic form, such as the tetra-ethyl-lead that was used to raise fuel octane ratings.
https://en.wikipedia.org/wiki/Tetraethyllead

The same is true of other heavy metal organics, such as methyl-mercury.
https://en.wikipedia.org/wiki/Minamata_disease

Many birds and reptiles consume grit and small stones for grinding food in their gizzard. (Dinosaur fossils, and crocodiles, have been found with gizzard stones). Lead shotgun pellets remain oxidised in water to form chemically stable lead compounds. If they are taken up by waterbirds as gizzard stones, the grinding process physically removes the chemically stable lead oxide surface layer, to reveal the reactive lead, that can then be bioaccumulated by the animal, to persist in the food chain. The transition from lead shot to iron shot, should reduce that source of potentially toxic lead in the environment.