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Environmental Impact of Wood Preservatives PCP/CCA/Cresol

I have an environmental chemistry course in which we are currently studying the environmental and health impacts of wood preservatives such as cresol, pentachlorophenol, and chromated copper arsenate.

Question 1:

For the 3 wood preservatives noted, would acidic vs. alkaline soil or water conditions cause more (or less) leaching or dissolution of these compounds. How do these compounds actually leach out of wood into the environment?

Question 2:

For the 2 organic preservatives, cresol and pentachlorophenol, and assuming that they are present in the wood, what happens when the wood is combusted? What are the combustion by-products of cresol and pentachlorophenol? Are they actually oxidized and destroyed?

Question 3:

Similar to Question 2, if cresol and pentachlorophenol are actually emitted to the ambient air as vapor, what role does photolysis play in the decomp of these organics? Do these complex phenol compounds favor oxidation or reduction reactions? What are the decomposition products when photolysis or oxidation occurs?

Question 4:

With respect to chromated copper arsenate, the arsenate has the formula AsO4(-3). Is there a way to render the arsenate ion less harmful? Can oxidation or reduction occur to change the nature of the arsenate ion?

Question 5:

What is meant by glycolysis?

Solution Preview

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Question 1:

For the 3 wood preservatives noted, would acidic vs. alkaline soil or water conditions cause more (or less) leaching or dissolution of these compounds.....I guess I am trying to understand the mechanism as to how these compounds actually leach out of wood into the environment?

It appears that acidic conditions increase the leaching of these compounds from wood. It is my belief that part of what keeps these compounds in the wood are electrostatic interactions that promote the formation of salts with in the wood.

The pKa of PCP is 4.98 (this is pretty acidic for an organic compound), and this increases the likely hood of formation of salts in the wood. Addition of acid would free the PCP from the wood allowing it to leach out. The pKa of cresol is about 10, so this effect would not be as great.

With CCA, from http://en.wikipedia.org/wiki/Chromated_copper_arsenate
"The chromium acts as a chemical fixing agent and has little or no preserving properties; it helps the other chemicals to fix in the timber, binding them through chemical complexes to the wood's cellulose and lignin. The copper acts primarily to protect the wood against decay fungi and bacteria, while the arsenic is the main insecticidal component of CCA."

These complexes could be broken down in an acidic environment, leading to a greater potential for leaching.

With regard to CCA...
From "http://en.wikipedia.org/wiki/Chromated_copper_arsenate"
"Recognized for the greenish tint it imparts to timber, CCA is a preservative that has been extremely common for many decades. Over time small amounts of the CCA chemicals, mainly the arsenic, may leach out of the treated timber. This is particularly the case in acidic environments. The chemicals may leach from the wood into surrounding soil, resulting in concentrations higher than naturally occurring background levels. A study ...

Solution Summary

The solution outlines the answers to questions referring to environmental fate and disposal of chemicals commonly used to treat wood (pentachlorophenol, copper chromium arsenate and cresol).

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