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Evaluation of the safety of new anti-fouling agents for use in Australian temperate waters

Final Report for the Department of the Environment and Heritage
S Duda, JH Myers and S Hoffman
Victorian Department of Natural Resources and Environment, 2003


Introduction

1 Introduction

The process of organisms settling on man-made surfaces is known as fouling. The organisms come from the water column as propagules searching for a hard substrate on which to complete their life cycle. The development of fouling begins as soon as a suitable substrate is immersed in the sea. Organic molecules present in the water start to adsorb on the surface leading to the settlement of microfouling organisms such as bacteria, fungi and protozoa. The development of fouling communities, proceeds with the establishment of macrofoulers such as macro algae, sponges, cnidarians, polychaetes, molluscs, barnacles, bryozoans and tunicates (Woods Hole Oceanographic Institution, 1952).

The primary mechanism for the spread between regions of infestation of fouling organisms is believed to be via ballast water and/or fouling of international shipping and other seaborne traffic (Hay, 1990; Sanderson and Barrett, 1989). It is estimated that fouling by marine organisms has a global cost of $3 billion annually (Jacobson and Willingham 2000). Fouling organisms accelerate surface corrosion and increasingly damage protective coatings. Organisms attached to ship hulls lead to increased frictional resistance of the ship therefore decreasing speed and increasing fuel consumption. It is estimated that a 1mm thick layer of algal slime will increase hull friction by 80% and fuel consumption by 17% (Fernandez-Alba et al. 2002). There is also greater need for ships to be out of action for hull cleaning which adds further to costs of the shipping industry (Evans 1999; Boxall et l. 2000; Evans et al 2000; Turley et al. 2000; Terlizzi et al. 2001).

Antifouling biocides are compounds that are incorporated into hull coatings of ships to be toxic to fouling species, preventing adhesion. Based on this, prevention of exotic pest species from colonising international harbours is one environmental advantage of antifouling biocides. Tributyltin (TBT) is a biocide that has been used commercially since the mid-1960s and as a coating can last up to 5 years (Terlizzi et al. 2001). Evans (1999) estimates greenhouse gas emission is reduced by up to 22 million tonnes of carbon dioxide and 0.6 million tonnes of sulphur dioxide as a consequence of TBT antifoulants.

Until recently, TBT was the most commonly used antifouling agent. However, it became clear that TBT rapidly spread from ships hulls and submerged structures to other environments and toxic effects were demonstrated in non-target invertebrates, micro- and macro algae (EPA 1993; Jacobson and Willingham 2000; Terlizzi et al. 2001; Johnson and Engey 2002). These effects towards non-target organisms became apparent in the late 1970's (EPA 1993), and it was found that many semi-enclosed water bodies with intensive shipping had become contaminated with TBT. These impacts induced many governments to restrict the use of organotin based antifoulants.

In 1982 France became the first country to ban the use of organotin antifoulants on vessels < 25m length. This approach was later adopted by other European countries, Australia and North America. In 1991, through the Mediterranean Action Plan, similar restrictions were also applied to the Mediterranean region (EPA 1993; Tolsa et al. 1996; Terlizzi et al. 2001). Following the restrictions imposed by separate countries, the International Maritime Organization (IMO) recommended a ban on the application of organotin antifoulants by 2003. This new proposal will prohibit the use of harmful organotins in antifouling paints used on ships and will establish a mechanism to prevent the potential use of other harmful substances in antifouling systems.

Under this proposal parties are required to prohibit and/or restrict the use of harmful antifoulant systems on ships flying the IMO flag, as well as ships not entitled to fly the flag, but which operate under their authority and all ships that enter a port, shipyard or offshore terminal of a party. By an effective date of January 1st 2003, all ships shall not apply or re-apply organotin compounds which act as biocides in antifoulant systems and by January 1st 2008 ships will either:

These proposals are part of a stepwise approach by the IMO, whereby all antifoulants which exhibit potentially harmful effects on the marine environment will eventually be banned (Evans et al 2000; Turley et al. 2000). Under the United Nations Convention on the Law of the Sea, the Commonwealth Government has an obligation to protect and conserve the marine environment. In a report to the Australian and New Zealand Environment and Conservation Council ( ANZECC) and the Ministerial Council on Forestry, Fisheries and Aquaculture ( MCFFA), the National Taskforce on the Prevention and Management of Marine Pest Incursions recommended an increased focus on the prevention of hull fouling as a vector for the introduction of introduced marine pests. The report also recommended the development of a cost effective, environmentally acceptable and safe alternative to TBT. Thus, the Australian Government is committed to assisting in the development of suitable alternatives to TBT.

Restrictions of TBT use have lead to a crucial need for new antifoulants, which are effective at preventing fouling, but cause no harm to non-target marine ecosystems. This has also led to an increase in the use of old fashioned antifoulants containing copper and/or the development of new paints incorporating booster biocides. These 'booster biocides' are used to improve the efficiency of the paints formulation, predominantly by inhibiting the primary growth of fouling organisms resistant to copper (Scarlett et al. 1999; Voulvoulis et al.1999; Terlizzi et al. 2001).

1.1 Organic booster biocides

The anti-fouling paint industry is actively working on the development of alternative biocides to fill the TBT niche. Organic booster biocides are being used as replacements for TBT. They are typically compounds that have been transplanted from a number of other uses, mostly from terrestrial herbicides and fungicides. These are usually used in conjunction with copper oxide coatings to improve the efficacy of the coating against copper resistant fouling organisms such as algal slimes (Voulvoulis et al. 1999).

The organic booster biocides have been selected largely on the basis of their physico-chemical characteristics (ie. short half-life, high sediment affinity. Based on this they were used, initially, without any monitoring or toxicity assessment (Evans et al. 2000). The reason why these biocides are accepted as alternatives is because they fulfil certain expectations of a biocide once present in the environment. These expectations are mostly founded on environmental persistence. Many of these compounds are now registered to be used in antifouling applications worldwide (International Coatings, November 2000).

1.1.1 Zineb

Zineb (Zinc ethylenebisdithiocarbamate) is a form of dithiocarbamate pesticide that was originally registered as a general use pesticide of low toxicity (Extoxnet, 1996). The compound is classed as practically insoluble in water (Merck, 1984). There were no marine toxicity assessments found in available literature that have been conducted on zineb. Most aquatic toxicological investigations have been conducted by Van Leeuwen et al. 1985 and 1986. Studies include a 48hr acute toxicity in the Cladoceran Daphnia magna, 96hr LC50s in Guppies Poecilia reticulata, 96hr EC50 on the green algae Chlorella pyrenoidosa and 15 min EC50 on the bacteria Photobacterium phosphoreum (Van Leeuwen et al. 1985). Of these organisms D. magna was the most sensitive with a 48hr LC50 of 0.97 mgL-1, the fish, P. reticulata were least sensitive, LC50 of 7.2 mgL-1 (Van Leeuwen et al. 1985). Other studied aspects include histopathy and embryolarval toxicity of Salmo gairdneri. Zineb affected no spinal cord damage on S. gairdneri fry at concentrations of up to 0.1 mgL-1 (Van Leeuwen et al., 1986). Uptake and retention of Zineb in S. gairdneri using 14C-labelling indicated that zineb was rapidly metabolised and excreted within 1-3 days of exposure. (Van Leeuwen et al. 1986).

1.1.2 Zinc Pyrithione

Zinc pyrithione (ZPT) is used as the active fungicide in some antidandruff shampoos. It is also, due to its low solubility in water used as an antifouling ingredient (Ranke and Jastorff, 2000). The mode of action for pyrithiones has been ascertained to "inhibit transport through membrane electrical depolarisation and that this depolarisation results from inhibition of the primary electrogenic H+-ATPase at an intramembrane or internal site" (Ermolayeva and Sanders, 1995).

ZPT is often used in antifouling mixtures with copper oxides or copper thiocyanate. The chelation of ZPT with copper creates aqueous Zn2+ and CuPT or copper pyrithione. CuPT is a more toxic form of the pyrithione complex and also likely to be more abundant because it has a lower dissociation constant than ZPT (Turley et al. 2000). This reaction may even occur with ambient concentrations of copper in natural seawater (Sadiq 1992). The toxicity of ZPT to aquatic organisms was 0.0046 mgL-1 for a 28 day LC50 with Juvenile rainbow trout (Okamura et al. 2002). Other toxicity tests by Goka, 1999, found that the embryotoxic effect of ZPT on the zebra fish, Brachydanio rerio, and the Japanese Medaka, Orysias latipes to be effective at 0.009 and 0.005 mgL-1, respectively. The comparable toxicity and low persistence of ZPT (half-life = 2-22 hr) is a clear advantage over TBT (Turley et al. 2000).

1.1.3 Diuron

Diuron is a relatively hydrophillic compound (log KOW = 2.7; HSBS database, 1997; sited in Thomas et al. 2000), and has a poor affinity to absorb onto the surface of particulate matter. Inputs of diuron to the marine environment are likely to be associated with paint chippings present in the sediment from the cleaning of hulls by high pressure hosing, and then allowing the washings to enter the marina (Thomas et al. 2000). This explains the source of diuron found in the sediment of only one site (Hythe marina, UK) of the twenty-seven that were sampled by Thomas et al (2000). Okamura (2002), concluded that diuron and the irgarol 1051 metabolite, M1, is more persistent than the parent compound Irgarol (1/2 life = 100 days). The only real toxicity assays conducted using diuron have used juvenile freshwater fish species S. gairdneri and flathead minnows (Call et al. 1987; Okamura et al. 2002). Diuron and Irgarol 1051 are banned for use in the application to pleasure craft as antifoulants in the UK and Denmark. They are however registered for use in the US and Canada (International coatings, 2000).

1.1.4 Seanine 211

Seanine 211 (also known as Kathon 5287) was the first organic booster biocide to be registered for use by the USEPA. It is an isothiazolone compound that is registered to be used in the UK and elsewhere (Voulovoulis, et al. 1999). The advantage of seanine 211 over other biocides such as TBT is that its half-life in natural seawater is in the order of hours, whereas TBT has a half life of several weeks to several months (Willingham, 2000). Seanine 211 has a log KOW above 6. (Meylan and Howard, 1995).The lipophillicity, which is assumed to be high, is not consistent with observed bioconcentration. The result of a 49 day bioconcentration study in bluegill sunfish demonstrated that the bioaccumulation of seanine 211 was essentially nil. A further advantage of Seanine 211 is that it and its metabolites bind strongly to sediment and once bound are essentially immobile (Jacobson and Willingham, 2000). This is expected to limit their bioavailability to certain organisms, the effects on benthic species is however uncertain (Jacobson et al. 1993).

With regard to the environmental impacts, seanine 211 exhibits non-specific acute toxicity to aquatic organisms. In this respect, it shows no clear advantage over TBT on a short-term scale (Fernandez-Alba et al. 2002).

1.2 Contamination of the Marine Environment by Biocides

These chemicals are intended to be environmentally less harmful compared to the previously used TBT based paints, however the adverse effects of these 'booster biocides' are poorly known and there is very little published work regarding their toxicity to marine organisms. This is probably due in part to their recent introduction and limited usage as antifoulants and their perceived lower toxicity compared to TBT. As a result they have had a reduced priority as compounds of environmental concern (Liu et al 1999; Evans et al. 2000; Voulvoulis et al. 2000; Terlizzi et al. 2001; Voulvoulis et al. 2002).

There are four main ways in which antifouling biocides can enter the environment:

  1. During application to structures and boat hulls. It is estimated that up to 30% is released to environment during spraying, the greater part of this ending up in harbours;
  2. Leaching from paint on hulls of vessels or structures;
  3. When paint is removed from structures and hulls; and
  4. When paint remnants are discarded.

However, actual input of each biocide to the aquatic environment depends on such factors as location of paint application, leaching rates and behaviour of biocides, methods in which residual antifouling paints are removed from hulls and structures (Johnson and Engey 2002).

It has become increasingly apparent that toxic compounds used in marine paints, previously and today, are responsible for some of the present marine pollution problems of coastal waters. Presently in Australia, authorities rely heavily on data obtained from overseas species to determine the risks associated with exposure to antifouling biocides in aquatic environments. Australia has its own unique and diverse ecosystems which may respond differently and may be more sensitive compared to European and American species. Therefore, it is not always appropriate to base guidelines on overseas species. In order to effectively protect and conserve Australia's marine environments, there is a great need to evaluate the safety of new antifouling biocides to local Australian temperate species.

The Marine and Freshwater Resources Institute (MAFRI) Queenscliff, Victoria was awarded 12 months of Natural Heritage Trust- funding to evaluate the safety of a range of new antifouling biocides that are currently used in Australia as TBT alternatives.

1.3 Aims and Objectives

The objectives of this study were to:

This will directly assist government, industry and community stakeholders to choose new, safer antifouling alternatives which will in turn, help to eradicate the use of dangerous antifouling agents such as TBT.