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Ok, so I am working on a project where I have to make a tax for manufacturers using non recyclable materials. So for this tax you multiply the weight (in kg) by how toxic the material is, this gives you an answer in pence. So I have a list of heavy metals that are dangerous to the environment but I don't know what one is the most toxic and the least toxic.

This is what I think the order from most dangerous to least dangerous is:

  1. Selenium (most harmful to the environment)
  2. Arsenic
  3. Mercury
  4. Copper
  5. Lead
  6. Cadmium
  7. Nickel
  8. Chromium
  9. Antimony
  10. Zinc (least harmful to the environment)

Could someone please share their opinion on this order and suggest a better order. Also could someone suggest a suitable number to multiply the weight by to get price in pence.

Thanks

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closed as off-topic by bon, Todd Minehardt, M.A.R., orthocresol, Curt F. Nov 29 '15 at 3:21

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    $\begingroup$ and I would also like a suitable number to multiply the weight by for each metal. This sounds like an important part of your project that you should not be asking someone else to do for you. I think part of the goal of your project is to devise your own scale and justify it. $\endgroup$ – Ben Norris Nov 28 '15 at 16:15
  • $\begingroup$ Can you at least put them in order because I really need that part $\endgroup$ – Alexander Baine Nov 28 '15 at 16:23
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    $\begingroup$ My answer below explains how figure out that order. It is not so straightforward that the average chemist has committed it to memory. I can group them into three categories (low, moderate, and high toxicity) by intuition, but I do not know the specific order. Given that effort has to be exerted to generate an order, it would be better for you to do it so that you understand your order when you need to explain it. In fact, I guess that the order you choose is less important than the logic of your rationale for this assignment. $\endgroup$ – Ben Norris Nov 28 '15 at 16:30
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This is probably a more complex problem than your instructor intended. In addition to the various metals having different toxicities, different compounds of these metals have different toxicities.

For example, nickel metal has low toxicity, but the compound $\ce{Ni(CO)4}$ is a poisonous, flammable, volatile liquid.

Likewise alkyl mercury compounds, e.g. $\ce{(CH3)2Hg}$ are vastly more toxic than the low solubility mercury salts like $\ce{Hg2Cl2}$.

If you just want to know about the pure metals, then this can be easier. Look up a Safety Data Sheet for each metal. It would be better if you pull all your SDS from the same source, that way they are all using the same data sources.

For example, here is a link to the SDS for mercury from Fisher Scientific. Section 12 contains ecological information, including LC50 (concentration that kills half of the population in the time period given) data for various aquatic organisms. Section 11 contains toxicological information, including LD50 (dose that kills 50% of the population) for various organisms.

The best way to do this is to try to find one set of data for all the metals with the same organism for the best comparison. Then, devise your scale.

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