Elsevier

Aquatic Toxicology

Volume 86, Issue 2, 31 January 2008, Pages 287-298
Aquatic Toxicology

Risks to human health and estuarine ecology posed by pulling out creosote-treated timber on oyster farms

https://doi.org/10.1016/j.aquatox.2007.11.009Get rights and content

Abstract

Five oyster farms in Port Stephens, Australia were studied to identify consequences of using creosote-treated posts and the risks posed by removing the posts. Gas chromatography coupled with mass spectrometry (GC/MS) was used to measure polycyclic aromatic hydrocarbons (PAHs) and phenols in sediments, timber, water and oyster tissue. Before posts were removed, the total PAHs in surface sediment on farms was 24.1 mg kg−1 dry weight. This increased to 45.5 mg kg−1 dry weight after the posts were pulled out and remained significantly higher 6 months later at 59.7 mg kg−1 dry weight. A similar increase was found in deeper sediments. The sediment attached to creosote-treated posts had a total concentration of PAHs of 484–2642 mg kg−1 dry weight, while the corresponding value for the sediment on tar-treated posts was only 30.7 mg kg−1 dry weight. The surface timber of creosote-treated posts had high levels of PAHs and an average post contained 43 g of PAHs. The total PAHs dispersed to the environment when a creosote-treated post was pulled out was at least 0.67 g. The main species were PAHs with low-molecular weights: fluoranthene, phenanthrene, pyrene, acenaphthylene and chrysene. Benzo(a)pyrene represented 1–10% of PAHs in most samples. Bioassays with creosote-contaminated sediment revealed that Sydney rock oysters (Saccostrea glomerate) and Pacific oysters (Crassostrea gigas) accumulated PAHs at (mg kg−1 wet tissue weight): 11.3–15.3 and 35.5–47.9, respectively, when exposed for 5 days to water with <1 μg l−1 PAHs. Wild oysters growing on creosote-treated posts had high levels of phenols (0.09–6.92 mg kg−1 wet weight) and PAHs (0.59–1.01 mg kg−1 wet weight). The dilemma posed by removing creosote-treated posts and dispersing carcinogenic, bioavailable contaminants needs to be managed in light of risks to human health and estuarine ecology.

Introduction

Oyster farming in New South Wales, Australia is based on the cultivation of the native Sydney rock oyster, Saccostrea glomerata (formerly Saccostrea commercialis) and to a lesser extent, on the introduced Pacific oyster, Crassostrea gigas. The farming of Sydney rock oysters is more than 100 years old and is the fourth largest form of aquaculture in Australia. Oyster sales were valued at A$32.6 million in 2005–2006. Nevertheless, annual production continues to decline from a peak of 17 million dozen oysters in 1976–1977 to 6.57 million dozen in 2004–2005 (DPI, 2006).

In 2004, faced with urban development of the coastline and the decline in oyster farming, the industry was required to commence a compliance program to clean-up oyster farms and remove derelict wooden structures. The program relied on a report on the environmental effects of rehabilitating derelict oyster farms in Port Stephens (Umwelt, 2001) which found that chemical contamination of sediments in abandoned oyster farms were comparable with other estuarine habitats (Ogburn, 2007).

Prior to ca. 1985, oyster farmers used timber posts which had been treated with either creosote (also known as coal tar creosote) or tar (also known as coal tar pitch). Creosote-treated posts are more resistant to decay than tar-treated posts and they can remain in estuarine waters for more than 40 years (personal observation). Nowadays farmers install tar-treated posts and recyclable posts. However, the proportion of existing wooden structures on oyster farms in New South Wales that have been treated with creosote is unknown.

Creosote is classified as a hazardous substance for occupational exposure (Deichmann and Keplinger, 1981, Chemwatch, 2006). There are over 300 chemicals in creosote, and the most toxic are phenols, cresols and polycyclic aromatic hydrocarbons (PAHs) (ATSDR, 2002). Many species of PAHs in creosote are known to be highly carcinogenic, mutagenic and toxic to marine organisms (Eisler, 1987, ANZECC, 2000, Peachey, 2003). The most potent carcinogens are benzo(a)pyrene (BaP), dibenzo(a,h)anthracene, dibenzo(a,h)pyrene and dibenzo(a,l)pyrene (p. A100, SCF, 2002). The toxicity profile for materials contaminated with creosote is determined by measuring the concentration of 16 species of PAHs which have been identified as Priority Pollutants by the US EPA (DEC, 2004).

PAHs are stable compounds with long residence times in the environment and they can be ingested by aquatic biota and bioaccumulate (ANZECC, 2000). Also, many invertebrates filter large volumes of water and are inefficient at metabolising and excreting PAHs (p. A7, SCF, 2002). Because of those properties, oysters and mussels have been used in many studies in various parts of the world as biomonitors of environmental contamination by PAHs and other persistent pollutants (Martin, 1992, Baumard et al., 1999, Fung et al., 2004, Lincoln-Smith and Cooper, 2004). Hence, so long as creosote-treated timber remains on oyster farms it represents a chronic source of hazardous pollution.

Conversely, the clean-up of creosote-treated posts from oyster farms could disturb contaminated sediments and lead to the dispersal of PAHs in estuaries. This may have ecological impacts, particularly since intertidal oyster farms are predominantly located in sensitive estuarine habitats that feature seagrasses (Zostera spp. and Posidonia australis) and mangrove habitats.

This paper describes the results of a study which aimed to quantify the levels of PAHs and phenols in timber, sediments, water and oyster tissue on oyster farms in Port Stephens. The findings were used to consider the risks to human health as well as ecological risks associated with creosote-treated posts, the clean-up of oyster farms and disturbance of contaminated sediments. The findings should be of interest to the oyster industry and agencies that manage oyster industries and estuarine habitats.

Section snippets

Study area and sample collection

Data was collected from five oyster farms in Port Stephens, Australia (33°0′S; 151°46′E). The main farm for the study is located near Mud Island, while the other farms are at Bundabah, Corlette Point, Stuart Island and Myall River. All farms use an intertidal method of culturing oysters and the foreshore is mangrove (Avicennia sp.) and seagrass (Posidonia sp. at Corlette Point and Zostera sp. at the other farms).

Each farm had a variety of owners in the period 1960–2006 and most of the oyster

Observations of oyster farms in Port Stephens

In Port Stephens oysters are cultured in trays and baskets that are supported by round (75–100 mm) or rectangular (50 mm × 75 mm) posts. Oyster posts were observed to be important refuges and habitats for a broad range of estuarine organisms, including algae, sponges, mussels, wild oysters, barnacles, worms, fish, crustaceans and birds. Most of the creosote-treated posts were observed to be in a deteriorated state and in many cases only 50–100 mm of post remained exposed above the sediment. The

Scope of the findings

The study of five oyster farms in Port Stephens, revealed that at two of the farms the majority of posts were creosote-treated, while at the other farms varying numbers of posts were creosote-treated. Although the farms in the study represent approximately 0.3% of the oyster-farming area in NSW, it is likely that creosote-treated timber is a problem for other oyster farms and possibly elsewhere in the world (p. 3, ATSDR, 2002; p. A6, SCF, 2002).

The study produced data which allowed for

Concluding recommendations

The findings of the study demonstrate that the use of creosote-treated posts results in substantial problems for oyster farmers and the environment. Eventually, farmers are confronted with the issue of removing degraded posts. Certain management practices should be considered to minimise impacts:

  • 1.

    The use of water pumps to blast away sediment from the butt of creosote-treated posts should be stopped. This activity causes massive disturbance to contaminated sediments.

  • 2.

    When old, creosote-treated

Acknowledgements

The author wishes to acknowledge the assistance and hospitality of the oyster farmers in NSW and thank Robert Kaziro, PhD for helpful discussions. The two reviewers provided excellent comments and enabled the manuscript to be substantially improved. The author declares a financial interest in oyster farming and thanks his daughters, Alison and Erika, for helping collect sediment samples.

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