Sediment Toxicity

Study

Below is the executive summary of the detailed study recently conducted on the environmental suitability of CCA-treated marine piling. The results will disprove any suggestions that treated piling is harmful to sediment-dwelling life.

Though the existence of abundant marine life on treated piling is evident at every low tide, a vocal few have suggested that leached preservative harms small sediment-dwelling creatures living near piling. This careful study, involving CCA-treated piling, disproves such suggestions.

This study was designed by an independent toxicologist (John Butala, diplomate) , reviewed by an independent expert on marine bioassay (Dr. Russell Schmitt, U.C. Santa Barbara), and conducted by an independent research organization (Springborn Laboratories, Wareham, Mass.). It was funded entirely by Hickson Corporation.

To the surprise of researchers, the leachate from treated piling caused lower mortality among the seabottom creatures than the leachate from untreated controls.

The objective of this study was to demonstrate the effects of 10-day exposure to sediments mixed with leachate (seawater) from CCA-C treated and untreated pilings on the benthic amphipod, Ampelisca abdita. The biological endpoint used to establish effects was organism survival during a 10-day exposure period. Leachate obtained during a 28-day (four 7-day intervals) period from CCA-C treated and untreated pilings was dosed onto two sediment types, high and low organic carbon (OC) sediments. The carbon characteristics of the sediment types were low OC (4% OC). Ampelisca abdita were exposed to sediment of each type dosed with one of three concentrations of leachate (i.e., 10%, 50% or 100% leachate). During this study, the components of the CCA-C treatment (copper, chromium and arsenic) were measured during the preparation of the leachate, in sediment mixtures and in overlying and interstitial water in the exposure vessels. The 10-day exposure was maintained under static conditions with continuous lighting to provide maximum exposure.

Measured amounts of copper, chromium and arsenic in naturally occurring water, sediment and in the leachates and treated sediments established that some variability occurred between measured amounts due to the behavior of the three metals in natural environmental conditions (e.g., seawater, sediment and wood). Although this variability was observed and was consistent with expectations of naturally occurring environmental conditions, reliable and useful trends were established which can be used to understand the general leaching and adsorptive properties associated with the CCA-C treated wood and subsequent exposure in natural marine environments.

Analyses for copper established that treated pilings released approximately 529 mg/m of exposed wood over 28 days. Mixing the leachate with LOC and HOC sediments resulted in adsorption of copper in the LOC sediment and to a slightly greater degree in the HOC sediment. Analysis of water in the exposure vessels demonstrated that the copper bound to both the LOC and HOC sediments remained bound and did not desorb into the interstitial or overlying water.

Analyses for chromium demonstrated that treated pilings generally released little or no chromium over 28 days. Mixing the leachate with LOC sediment resulted in negligible uptake of chromium into sediment and only a minimal amount of chromium adsorbed to the HOC sediment. Analyses of the interstitial water in the exposure vessels demonstrated that chromium present in the sediment generally did not move into interstitial water but did move into overlying water from both LOC and HOC sediments.

Analyses for arsenic demonstrated that approximately 59.5 mg arsenic/m2 of treated wood surface area leached from the treated pilings. Arsenic did not appear to adsorb onto sediment of either type and, in almost all cases, was not observed in interstitial or overlying water.

Comparison of the survival data for the exposures conducted from the untreated and treated wood pilings and the survival of the organisms maintained under control conditions established that leachate from untreated pilings adversely affected organism survival while leachate obtained from CCA-C treated wood pilings did not adversely affect organism survival. The primary constituents of the CCA-C treated wood pilings were not present in the leachate at concentrations which would adversely affect the survival of the organisms. The adverse effects observed during this study were presumed due to exposure to naturally occurring compounds (e.g., terpinene, camphene, pinene) present in wood prior to treatment with CCA-C. Since the effects were only observed in leachate prepared from untreated wood pilings, it is believed that the natural toxic components of the wood were extracted or altered during the process used to treat wood pilings with CCA-C. As a result, the release rate or the bioavailability of these natural toxins was reduced for the treated pilings relative to those not subjected to the CCA-C treating process.