Totara Lagoon

​PCP and Dioxin Investigation: Totara Lagoon, Bittern Creek, Ruatapu Dredge Pond

This report presents the results of an investigation into possible environmental impacts from PCP and dioxins on aquatic environments in the Ruatapu area, including Totara Lagoon, Bittern Ck mouth, and the Ruatapu dredge pond. This investigation focussed on the human health threat posed from the consumption of eels. Consideration was also given to the likely impacts on the aquatic ecosystem and sought to assess the level of chemical contamination in water and sediments.

It is assumed that the source of PCP and dioxins comes from historic timber treatment activities at the sawmill in Ruatapu. Fletchers constructed the original sawmill at Ruatapu in 1965, passing ownership to Carter Holt Harvey in the late 1980’s, and the site is now owned independently by Westco MTP Ltd (as of 2010). The timber treatment chemicals used on site were boric and antisapstain compounds. Up until 1988 the antisapstain treatment involved sodium pentachlorophenate. Potential has existed for the transportation of pentachlorophenol (PCP) to aquatic environments beyond the sawmill boundary, via leachate and sediments associated with stormwater run-off.

Low levels of PCP were found in sediments, and in eel bile.  If PCP was high in both sediment and eel bile, it would have indicated that gross contamination was present and exposure was ongoing, but this was not the case.  PCP is not bio-accumulative, but dioxins are, so dioxins were also analysed for in samples of eel flesh. As well as their bio-accumulative nature, dioxins break down slower, adsorb more readily to sediment, and are more toxic than PCP.  Eels can be long-lived, and their flesh is likely to be eaten by other eels when they die, and hence recycle contaminants. Because eels are high in the food chain they would be expected to have one of the highest dioxin concentrations of any animal in the ecosystem.

The results showed that there was no discernible differences between dioxin in the lab blanks and eel flesh, and considering the many non-detects for the more crucial congeners (eg Hx, Hp and OCDD), there is unlikely to be any significant dioxin contamination in the lagoon. Because of this, it is not necessary to calculate any dietary intake restrictions from these results for eel consumption.

The dredge pond was the only location where high levels of PCP could be definitively affirmed. There is no surface discharge from this pond where contaminated sediment and water might migrate and contaminate other areas, which has also been confirmed by other investigations in the area. The pond is located in bush and there are no public tracks leading to it. The sides of the pond are steep and lead into very soft sediment. No eels were caught in the pond despite efforts to catch them, and given that there is no outlet, there is no way fish can colonise the pond. There would appear to be no real opportunities for contact recreation and food gathering at the pond i.e. there are no complete exposure pathways to people, or to areas beyond the pond. Hence PCP, and any other associated contaminants, should present no environmental threat beyond the dredge pond itself. It is important to note however that due caution is taken should any further development involving movement of soil, sediment or water from the area around the pond be considered.

Further testing in the dredge pond was conducted in 2010. One sediment sample was taken from the eastern side of the pond, approximately 100 m from the inflow at the southern end. Sediment levels of PCP and boron in this sample were 0.09 mg/kg and 9.5 mg/kg, respectively.  A water sample was also collected from the same location and analysed for PCP and boron. There was no detectable PCP (< 0.00001 mg/L), and boron was 0.013 mg/L. Water quality guidelines for boron are  0.37 mg/L.

Click here to download the Totara Lagoon PCP and Dioxin Investigation Report 2009 (PDF, 3.0MB)

Page reviewed: 14 Apr 2014 4:42pm