Wood preservation facilities, chromated copper arsenate: chapter B-3

3. Environmental Effects

3.1 Aquatic Toxicity

In considering the aquatic toxicity of CCA, the following points should be borne in mind:

• Ratios of copper, chromium and arsenic in soil and runoff water from CCA facilities are not necessarily consistent with their ratios in the original CCAworking solutions. Depending on various factors, it is possible that only one element may be predominant. As a result, the toxicity of each element, in addition to the toxicity of the CCA mixture, should be reviewed.
• Valence changes of arsenic, chromium or copper may occur within the environment, and those changes may reduce or enhance the toxicities of the elements. There have been no studies reported in the literature on valence interconversion of copper, chromium or arsenic in soil or groundwater at--or in surface runoff water from--CCA facilities. Chromium is released into water and soil as trivalent chromium, but the concentration of trivalent chromium is the lowest of the three metals, partly attributed to the fixation process in the wood structure. Arsenic is leached into soil and water as pentavalent arsenic (8). A limited study was carried out for the purposes of this document to assess arsenic speciation. The study indicated that samples of soil and water in the vicinity of CCA facilities contained at least 97% of the original pentavalent form of arsenic (9).

Canadian limits for arsenic, chromium and copper in aquatic environments are listed in Table 3, and these limits are subject to change from time to time. Recurrent review of these limits is recommended.

All of the guidelines and limits in Table 3 are based on total concentrations of arsenic, chromium or copper and reflect the recommended approach of many scientific reviews. These reviews indicate that the current state of knowledge does not enable water quality limits to be based on either valence state or dissolved fractions in water (10, 11, 12, 13).

Provincial guidelines are applicable and should be consulted. Provincial guidelines may differ from or be more specific than national guidelines. Provincial regulations may require additional measures that may enhance, but not reduce, protection.