Timber treatment Chemicals (including creosote)
Entry into the marine environment
Wood deterioration can be caused in a number of
- fungal attack;
- insect attack;
- mechanical wear and fire.
There are numerous active ingredients (in excess
of 50) registered for use in the UK (PSD/HSE 1998)
which can be broadly grouped into three categories:
- organic solvents;
- water borne; and
Organic solvent based preservatives most commonly
comprise either one or a mixture of some of the
- pentachlorophenol laurate;
- 2-phenyl phenol;
- metal naphthenates and bis (tributyltin)oxide
(TBTO), dissolved in an organic solvent usually
of the white spirit or kerosene type.
In addition to the active ingredients, additives
such as resins, colouring agents and water repellents
may also be added (HMIP 1992).
Water borne preservatives usually comprise a mixture
of inorganic salts dissolved in water. The water
borne preservative group is dominated by the copper-chromium-arsenic
(CCA) preservatives which frequently consist of
a mixture of copper sulphate, sodium dichromate
and arsenic pentoxide. Copper (see Section B7) and
arsenic (see Section B9) are the principal pesticidal
agents while the dichromate fixes the copper and
arsenic in the wood. The preservative is mixed with
water at the treatment site. The advantage of the
CCA wood preservative is that they bind very tightly
to the timber, giving the treated timber a long
life even when immersed in water. Other compounds
used in water borne preservative include sodium
arsenate; disodium octaborate and sodium salts of
chlorinated phenols, boron based compounds and quaternary
ammonium compounds (Williams 1994).
The third type of preservative is creosote, a blend
of distillate oils, mainly from coal tar with boiling
points ranging from 200 - 400oC. It contains
a high proportion of polyaromatic hydrocarbons (PAHs),
together with a few percent of tar acids (phenolic
derivative). While the use of creosote has fallen
since the early 1970s, it still accounts for a significant
proportion of the UK market (Williams 1994).
The use of timber treatment chemicals falls into
three main categories:
- industrial pre-treatment of timber (pressure
and vacuum plants and non pressure processes such
as immersion plants);
- remedial treatment (so called professional use);
- domestic (DIY) use by retail customers.
Inputs of timber treatment chemicals into the aquatic
environment can emanate from point and diffuse sources.
Point sources include wastewater arising during
the manufacture of active ingredients and formulations;
where treatment plants use formulation with volatile
ingredients, release to air may occur, and these
may enter the aquatic environment through atmospheric
deposition. There is the potential for spillages
or releases, resulting from either bad on-site housekeeping
or through accidents.
Of the three main use categories, industrial pre-treatment
of timber represents the most likely point source
of timber treatment chemicals due to the large quantities
of chemicals handled at the pre-treatment sites.
Diffuse sources may also be significant for some
preservatives, such as creosote used in remedial
and domestic situations.
Williams (1994) reviewed timber treatment chemicals
in order to identify chemicals with a high to medium
risk to the aquatic environment for the purpose
of EQS development. From the list of over 50 active
ingredients registered for use in the UK, 20 were
identified for the risk assessment.
Selected chemicals used in the timber treatment
industry (from Williams 1994)
with existing or proposed (UK/EU) EQSs
with no existing or proposed (UK/EU) EQSs
salts (copper sulphate, sodium or
potassium dichromate and
pentoxide or similar mixtures)
(PAHs, tar bases, tar acids)
phenol (and salts)
soaps (versatate, octoate, acypetacs, naphthenate)
* EQS development in progress
Williams (1994) concluded that the substances of
greatest concern in terms of their usage, aquatic
toxicity, persistence and bioaccumulation were CCAs
and tributyltin naphthenate (TBTN) whilst creosote,
zinc versatate, zinc octoate, acypetacs zinc and
copper naphthenate were of medium concern.
CCAs and copper naphthenate are likely to exert
their toxic effect due to the dissociation of copper
and, therefore, the existing standards for copper
(EQS) were considered sufficient for the protection
of the aquatic environment (see Section B7). Similarly,
the existing EQSs for TBTO and zinc were considered
sufficient for the protection of aquatic life from
TBTN and zinc compounds.
Creosote was the only remaining substance of concern
with no existing EQS. The remainder of this profile
concentrates on creosote using information from
Creosote typically comprises 85% PAHs, 10% phenols
(or tar acids) and 5% tar bases. Coal tar creosote
usually consists of liquid and solid aromatic hydrocarbons,
such as guaicol, phenol, cresols, pyrol and pyridine.
The major PAH constituents are acenaphthene, anthracene,
benzanthracene, fluoranthene, fluorene, phenanthrene
and pyrene, although as many as 36 have been identified.
Recorded levels in the environment
Creosote is not monitored under any national monitoring
programme and would probably only be measured close
to known sources. Concentrations of individual PAHs
are occasionally measured in sediments and biota
(see Appendix D). Contributions from creosote may
add to these close to known sources.
Williams (1994) reported that creosote oil had
been recorded in biota (molluscs and crustaceans)
and that lipid concentrations of 1,046 (mussels),
459 - 3,254 (periwinkles), 202 - 354 (whelks) and
459 ppm (clams) had been measured.
Fate and behaviour in the marine
Creosote is of low solubility and stable in water.
Only about 9% may dissolve and be transported away
from point sources (Williams 1994). Some of the
constituent PAHs have been shown to accumulate in
sediments. The major fate processes are believed
to be biodegradation and photolysis, depending on
light availability. Complete breakdown may take
between 3-12 months.
Effects on the marine environment
Toxicity to marine organisms
An exhaustive literature review on the toxicity
of creosote to marine organisms has not been carried
out for the purposes of this profile. The information
provided in this section is taken from existing
review documents (Williams 1994). The most sensitive
organisms have been identified.
Creosote appears to be of moderate to high toxicity
to marine fish and of high toxicity to marine invertebrates
with 96-hour LC50s of 0.56 - 4.42 mg l-1
and 0.018 - 0.24 mg l-1 respectively.
An EQS for creosote has not been developed because
of the heterogenous nature of the mixture and associated
Williams (1994) report a BCF of 0.6 for the dissolved
fraction in a water body, indicating that it is
not likely to be bioaccumulated in aquatic organisms.
Potential effects on the interest
features of European marine sites
Potential effects include:
- toxicity of creosote in the water column to
marine invertebrates and fish;
- physical effects of a spillage of large quantities
of creosote may be similar to the effect observed
for oil and petrochemicals.