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Retreatment of Spent Creosote-Treated Wood with Copper
Hydroxide and Sodium Tetraborate |
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Bessie Woodward
Microbiologist USDA Forest Service Forest Products Laboratory William Abbott
Pole Maintenance Company Michael West
Delta Research Abstract
Southern pine sapwood blocks, treated with creosote at
sub-threshold level, were retreated with either copper hydroxide or sodium
tetraborate and evaluated by laboratory soil-block tests to determine
efficacy of retreating creosote-treated wood with short chain amino copper
compounds and borates. The unexpected copper synergism with creosote confirms
that amine copper complexes from copper hydroxide are highly synergistic with
creosote for controlling Neolentinus lepideus, the creosote-tolerant
fungus. The compatibility of copper hydroxide and sodium tetraborate
decahydrate with creosote suggests that these chemicals can be used
effectively for retreatment of creosote poles. Retreatment of Spent Creosote-Treated
Wood with Copper Hydroxide and Sodium Tetraborate Introduction
Creosote, one of the most potent fungicides, has an extremely
complex composition containing phenols, aromatic hydrocarbons, nitrogen
bases, and other toxicants. But as potent as this fungicide is, some fungi
are not deterred by this mixture of compounds. In the search for compounds
that may enhance its fungicidal properties, creosote has been fortified with
copper naphthenate (Duncan and Richards, 1950), pentachlorophenol (Duncan and
Richards, 1950 and Snoke, 1954), chlorinated hydrocarbons (Fahlstrom, 1971),
and more recently with synthetic pyrethroids (Cragg and Eaton, 1997). The
target for these enhancements has been to provide protection for marine
piling against Limnoria, Teredo, and pholads. Understanding compounds that may be useful
for synergism when combined with creosote must include an understanding of
the ionic nature of these compounds. Copper naphthenate is frequently found
in wood protection chemicals, where it is recommended for use in combination
with both creosote and pentachlorophenol. This compound contains cationic
copper and the anionic naphthenate radical. It is possible for the copper
element in copper naphthenate to be extremely synergistic with creosote, yet
have that synergism reversed due to antagonism between the naphthenate and
the creosote. |
Duncan
and Richards (1950) proved that copper naphthenate was not synergistic with
either creosote or pentachlorophenol. Snoke (1954) determined that when creosote
is fortified with pentachlorophenol, the increased effect of the preservative
system is related directly to the amount of pentachlorophenol added to the
mixture. Although this is used and is highly effective, it is also highly
corrosive to treatment plant equipment when any water is present. We hope to
find a copper pesticide that can be used with creosote emulsions to give a
synergistic effect against creosote- and copper-tolerant fungi and that is
not corrosive. Methods and Materials
The experimental approach followed AWPA E10: Standard Method for
Testing Wood Preservatives by Laboratory Soil-block Cultures. Wood
§
Three-fourth-inch
cubes of southern pine sapwood were used for the wood substrate. §
Blocks were treated with chemical listed in Table 1 in a
two-phase process (Table 2). Fungi
§
Neolentinus lepideus (M534), a creosote-tolerant
fungus §
Gloeophyllum trabeum (M617), an arsenic- and
phenolic- tolerant fungus §
Postia placenta (M698), a copper-tolerant fungus |
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Results
Figure 1. Synergism of Cu(OH)2 with Creosote in
Unleached Soil-blocks
Figure 2. Synergism of Na2B4O7
with Creosote in Unleached Soil-blocks
Discussion DeGroot and Evans (1999) showed
statistically that with creosote, increased retention levels increased
product longevity in the field. But in a health conscious society,
overloading a product with a chemical that bleeds is not a |
wise choice. From our data we
were able to confirm that amine copper complexes from copper hydroxide (Fig.
1) and borates (Fig. 2) are highly synergistic with sub-threshold levels of
creosote for control of the creosote-tolerant fungus N. lepideus. Duncan
and Richards (1950) determined that copper naphthenate was not synergistic
with either creosote or pentachlorophenol, and Fahlstrom (1971) found that
chlorinated hydrocarbons were also not synergistic with creosote. Our results
show an unexpected copper synergism with creosote, which confirms that amine
copper complexes from copper hydroxide are highly synergistic with creosote
for controlling N. lepideus, the creosote-tolerant fungus. The
compatibility of copper hydroxide and sodium tetraborate decahydrate with
creosote suggests that either of these chemicals (creosote-copper hydroxide
or creosote-borate) can be used effectively for remedial treatment of
creosote poles. Conclusions
From the results in Table 3, we can make the following
conclusions: §
Creosote is effective against decay caused by Gloeophyllum
trabeum and Postia placenta. §
Cu(OH)2 at the lower retention and Na2B4O7
at the higher retention are effective against decay caused by Neolentinus
lepideus. §
For blocks treated with Cu(OH)2, an average weight
loss above 30 percent was achieved with G. trabeum and above 50
percent with P. placenta. §
Weight loss was above or comparable to controls in blocks
treated with Na2B4O7 and exposed to G.
trabeum and §
Weight loss significantly decreased in blocks that were
retreated with Cu(OH)2 and Na2B4O7
when exposed to References
AWPA (2001). Standard method of testing wood
preservatives by laboratory soil-block cultures. E1091. American Wood
Preservers Association. Standards 2001, 426–435. Baechler, R.H., and H.G. Roth (1956). Laboratory
leaching and decay tests on pine and oak blocks treated with several
preservative salts. Amer. Wood-Pres. Assoc.: 1–10. Cragg, Simon M. and Rodney A. Eaton (1997). Evaluation
of creosote fortified with synthetic pyrethroids as wood preservative for use
in the sea. II. Effects on wood-degrading micro-organisms and fouling
invertebrates. Material und Organismen. 31(3): 197–216. DeGroot, Rodney C. and James Evans (1999). Does
More Preservative Mean a Better Product? Forest Products Journal. 49: Duncan, Catherine G. and C. Audrey Richards
(1950). Evaluating Wood Preservatives by Soil-Block Tests: 1. Effect of the Carrier on
Pentachlorophenol Solutions. 2.
Comparison of a Coal Tar creosote, a Petroleum Containing Pentachlorophenol
or Copper Naphthenate and Mixtures of Them. AWPA Proceedings. 46: 131–151. Fahlstrom, George B. (1971). Additives to Creosote
for Improved Performance in Marine Piling. Forest Products Journal: 67:
131–139. Snoke, Lloyd R. (1954).
Soil-Block Bioassay of a Creosote Containing Pentachlorophenol. Forest
Products Journal. 4(1): 55–57. |
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