Viewpoint

Dangerous Chemicals

By Tim Frederikson

A timber treatment company made the news recently when it was charged with polluting neighbouring properties. Timber treatment waste gives an attractive green colour to areas where it is used or dumped, but the pretty green can be a deadly problem.

Timber is treated for a number of reasons. Chemicals are added to timber to prevent sap staining the finished product, to prevent the timber being attacked by fungal infections and to reduce the likelihood of insect damage.

Chemicals used include sodium pentachlorophenate, copper 8-hydroxyquinolate, boric acid, creosote, methyl bromide and and a number of CCA type preservatives. CCA preservatives involve copper salts, chromium salts and arsenic. Often, dichromates of sodium or potassium are substituted or added to the brews, as are oxides of zinc or fluorides of sodium.

All these chemicals have their own particular safety hazards. Even the light organic solvent preservative, introduced in 1979 to reduce CCA pollution and increase efficiency, is not totally safe because of its flammability. A number of these chemicals have been withdrawn from use in agriculture because of their long-term residual characteristics, but still pose real problems for the environment.

In treating timber, the wood is loaded into large steel pressure cylinders and flooded with chemicals under pressure. The chemicals are absorbed by the timber and then the pressure is reduced and the liquid drained. A vacuum created within the cylinder assists the removal of surplus chemicals. The timber is then removed and stood on a drip pad until any further surplus chemicals have stopped seeping from it.

Some plants merely spray the timber, but this requires a longer time standing on the drip pad and is incompatible with an industry which measures efficiency in the amount of timber processed.

The pollution problems arise from the drip pads and the disposal of used or waste chemicals. In many parts of the country, timber treatment plants have been built above water supplies or aquifers. Surplus chemicals from timber moved off the drip pads prematurely can soak through the unprotected ground and pollute those supplies.

The CCA chemicals are particularly deadly, as they consist of extremely high concentrations of heavy metals, acid wastes and arsenical compounds. These blow away plant, fish and animal life in their path. They do not biodegrade and cannot be recycled.

Cowboy disposal operators drop them anywhere they can, out of the public eye. Sometimes they are in drums, sometimes the only evidence is a bright green stain at the end of a country road. Refuse tips are not meant to handle the wastes due to their toxicity and propensity for leaching into and along the substrata. This country does not have the technology to incinerate or destroy these wastes in the quantities in which they are produced, although chemical neutralisation is possible to a small extent. Many plants, however, prefer to dispose of their wastes without such added costs...

Tim Frederikson is a chemical safety consultant.