Introduction

CCA can cause cancer
Pathways of Human Exposure to CCA-Treated Timber
International Research
Uncertainties
References

CCA can cause cancer

Copper, chromium and arsenic are all heavy metals which means that they are metallic chemical elements that have a high density and are toxic to humans at very low concentrations. Arsenic is of most concern in this context because there is evidence from several published scientific studies (see for example Children's Health section) that the arsenic leaches out of CCA-treated wood over time.

According to the World Health Organisation (cited in Sharp and Walker, 2001: 2) and the US Environmental Protection Agency (Office of Pesticide Programs, 2002b) arsenic is “a known carcinogen and is acutely toxic”. It can cause various cancers including lung, bladder and skin cancer, as well as non-cancer damage, including reproductive and neurological problems (CPSC, 2003b: 14). People can be exposed through touching the timber as surface arsenic sticks to human skin (Gray and Houlihan, 2002: 9). It can be absorbed by the skin (less likely), breathed in with wood dust particles, or transferred to the mouth, for example by subsequent handling of food (CPSC, 2003b: 10).

International Research

There is a wide range of research from international sources documenting the effects of cumulative exposure to arsenic:

• the US Consumer Product Safety Commission (CPSC, 2003a) cites studies showing high levels of arsenic in drinking water are linked with increased incidence of lung and bladder tumours in Taiwan.
• Lee et al (2003) report that in rats exposed to CCA, arsenic was detected in lung, liver, heart and the viscera, and copper was detected in the liver.
• Research on toenail clippings by Beane Freeman et al (2004) found an increased risk of melanoma for participants with arsenic exposure, measured through toenail arsenic concentrations. The majority of participants who reported they had been exposed to arsenic on the job had the highest arsenic levels of all participants, “indicating that occupational exposure may be an important source of arsenic contamination”.
• Kaltreider et al (2001) found that, at extremely low levels of exposure, arsenic is found to alter hormonal function in the 'glucocorticoid' system, which influences physiological processes, such as growth control, glucose regulation and protein metabolism.

Uncertainties

Nevertheless there is not enough epidemiological evidence to ensure agreement about the health impacts of CCA exposure. This is explained by Belluck et al (2003) as due to:

• Physicians not being trained to recognize soil arsenic exposures;
• No mandatory surveillance and reporting system (or tabulation of data) for soil-induced health impacts;
• Non-carcinogenic effects (eg dermal, cerebrovascular and cerebral effects) being attributed to other causes;
• Adverse health effects from exposure not being observed until the damage is advanced; and
• Arsenic being associated with more than thirty different health effects.

The authors are aware that correlating health impacts with soil-related arsenic exposures in highly mobile populations is very difficult, but reiterate that there is not sufficient data to rule out elevated surface soils levels of arsenic as a cause of human morbidity or mortality (Belluck et al, 2003).

The situation is exacerbated by the fact that during the decades that timber has been treated with CCA, there has been no real effort collate the long term health records of people working in the industry. The Australian Pesticides and Veterinary Medicines Authority (APVMA) is only now belatedly recommending that health data be kept by the industry.

A further uncertainty is whether the CCA components (copper, chromium and arsenate) in combination differ from effects caused by an exposure to each metal separately. For example, the presence of chromium and copper may alter the health impacts of the arsenic, such as absorption, retention and excretion (US EPA, 2003). Also some people are more sensitive to chemicals than others (Buckland, 2005).