risk-benefit analysis and case study on tributyl tin

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International Biodeterioration & Biodegradation (1994) 401~412 Copyright © 1995 Elsevier Science Limited Printed in Great Britain. All rights reserved

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Risk-Benefit Analysis and Case Study on Tributyl Tin

Lesley Moore & Meg Postle

Risk & Policy Analysts Limited (RPA), Warren House, Beccles Road, Loddon, Norfolk, NR14 6JL, UK

ABSTRA CT

The Risk-Benefit Analysis (RBA) methodology was developed for the Department of the Environment to assist in the evaluation of regulatory choices concerning hazardous chemicals. RBA considers the risks (human and environmental) and benefits (direct and indirect) associated with the use of a hazardous substance and aims to express these in monetary terms. Through detailed consideration of the existing regulatory regime and the effects of possible regulatory changes, RBA highlights (and quantifies) the trade-offs which would be involved.

The tributyl tin (TBT) case study considered the use of TBT in antifouling paints. Through the application of the RBA methodology it looked at the impact (in the UK and the EC) of a ban on the use of TBT and of stricter controls at docks involved in the repainting of ships. Valuation of the economic benefits associated with the use of TBT enabled the risks associated with its use to be implicity valued.

I N T R O D U C T I O N

The risk-benefit methodology was developed for the Environment Protection Economics Division of the U K Depar tment of the Environ- ment as a new and balanced approach towards decision-making on control of hazardous substances. The methodology is a decision aid which provides a rational f ramework for weighing up the advantages and disad- vantages of alternative regulatory choices. It is based on the principles of

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cost-benefit analysis and, as such, aims to express all of the potential effects (economic, environmental and human health) of a control measure in monetary terms. In so doing it makes the trade-offs between these effects explicit and thus sets out the implications of a control decision.

The methodology was developed by a team comprising of economists, toxicologists and ecologists 1 and its application was tested on two case study chemicals, one of which was tributyl tin (TBT). The study was undertaken in the second half of 1992 and is reported in full in Risk- Benefit Analysis of Hazardous Chemicals (Risk and Policy Analysts et al., 1992).

TBT was chosen as a case study chemical for three reasons. Firstly, there was widespread concern over its environmental effects. Secondly, as a result of this concern, there was a wealth of research data which would be of use in the analysis. Finally, it was felt that there was the potential for further international controls on the use of TBT and that the full implications of any such controls should be examined.

The economic basis of RBA

Risk-Benefit Analysis (RBA) is a form of economic appraisal and is based on the principles of cost-benefit analysis 2. It compares different control options by quantifying and valuing the costs and benefits associated with them. Economically, an option is justified if the benefits of that option exceed the costs. The best option is that which has the greatest net benefits.

For any given control option there will be a range of associated costs and benefits. For a ban on a hazardous substance, for example, there will be "private" costs to producers and consumers (and others) which will arise from its loss of use. In addition, there will be the "social" benefits (environmental and human health) which accrue as a result of the ban. RBA considers, and attempts to value, both these private costs and social benefits. As the latter are not normally valued in monetary terms, economists have developed a range of techniques for their valuation 3 (those which relate to TBT are discussed below).

1The economic aspects of the study were undertaken by RPA with the assistance of Professor Huw Dixon of the University of York. The environmental risk assessment was undertaken by Acer Environmental and the human health risk assessment by Professor Anthony Dayan, Director of Toxicology at St Bartholmews Hospital. 2Government guidelines on cost-benefit analysis are given in Economic Appraisal in Central Government: A Technical Guide to Government Departments (HM Treasury, 1991). 3As a first guide to valuation techniques see Policy Appraisal and the Environment (Department of the Environment, 1991).

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In addition to private and social costs and benefits, there may be other effects which arise as a result of a control on the use of a substance. These may relate to employment or to the distribution of risks and benefits, for example. Economic analysis does not consider such distributional issues (only the overall level of costs and benefits to the nation as a whole are considered). Clearly such issues may be important in the political sense, however, and they are therefore identified by an RBA for input into the decision-making process.

THE M E T H O D O L O G Y

The risk-benefit methodology for hazardous substances involves the following stages:

(i) Identification o f key issues: this is the initial scoping exercise which defines the decision problem. Reviews of available litera- ture and consultations with relevant experts, trade associations and government departments are undertaken to determine the key issues surrounding the problem and the key impacts for analysis.

(ii) Collection o f base data: in order to undertake the analysis, data are required on levels of production and the main manufacturers (both domestic and importation sources); current levels of consumption overall and in specific uses; trends in production and consumption (taking into account past, current and expected legislation); and potential substitutes, their availability, efficacy and associated risks.

(iii) Identification o f life-cycle releases: to determine the risks associated with a hazardous substance and the control options to be considered, it is necessary to identify the stages at which releases occur. These stages are broken down into production and any further processing or formulation activities; storage and handling; use of the end-product containing the substance; and disposal of that end-product.

(iv) Environmental risk analysis: to predict the effects that a hazardous substance will have on the environment, consideration needs to be given to the physical, chemical and biological prop- erties of that substance; environmental release pathways and environmental fate; and environmental concentrations and toxi- city. These factors also need to be considered for substitute chemicals.

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Human health risk analysis: this is based on the findings of the environmental risk assessment. The likely human exposure levels through different pathways (direct contact, inhalation, drinking contaminated water, eating contaminated food, etc.) are deter- mined and combined with information on the toxic effects in man to calculate health risks to different target populations. Economic assessment: the economic costs and benefits associated with control of the hazardous substance are then estimated. These include private sector costs and benefits and external (environmental and health) costs and benefits. Evaluation of trade-offs: this final stage of the analysis highlights the key differences between alternative control measures and the implications of each. Consideration is given to the activities of concern and associated risks; the characteristics of the risk; the levels of risk reduction associated with the use of substitutes; the efficacy of substitutes; and the economic and social costs of control and their distribution across different groups.

THE TRIBUTYL TIN CASE STUDY

TBT is primarily used as the active biocide ingredient in antifouling (AF) paints and is also used as a wood preservative; this paper deals only with the marine applications of TBT. Within these AF paints, TBT acts as a toxicant to control the growth of seaweeds, barnacles and tubeworms on the hulls of ships.

TBT was selected as a case study chemical because there was widespread concern about its impact on the aquatic environment and, as a result, there had been a considerable amount of research into its environmental effects 4 and the financial implications of the withdrawal of TBT from the marketplace [see for example Milne, (1990) and The Marine Painting Forum, (1992)]. In addition, there was the potential for further controls on the use of TBT at an international level.

For TBT in AF paints, consideration was given to two levels of control, namely, the imposition of dock management controls for the collection of contaminated wash waters, and a total ban on the use of paints containing TBT. The TBT case study focused on evaluation of the trade-offs associated with UK controls, although the implications of EC controls were considered where possible.

4See Risk & Policy Analysts et al. (1992) for a comprehensive list of references.

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Identification of key issues

Contact was made with almost 50 organisations, including makers and formulators of TBT, paint manufacturers, dockyard and shipping (fleet and ferry) operators, trade associations, environmental groups (such as the Shellfish Association of Great Britain), Government agencies and other organisations involved in relevant research. This consultation confirmed that the key issues were the effects of TBT on the aquatic environment and the cost implications associated with a ban on its use (e.g. more frequent repainting and dry docking and increased fuel consumption).

As well as identifying key issues, this initial consultation exercise ensured that all interested parties were informed of the study and its aims. In particular, this facilitated the collection of data for the study, almost all of which was provided by industry (as personal communications).

Collection of base data

Data collection established that TBT is not manufactured in the UK but is imported for formulation or as the finished product. The EC manu- factures 8000 tonnes per annum (tpa) of TBT (Haskoning, 1989). By far the largest use of TBT in the UK is in the production of AF paints, which accounts for around 90% of TBT consumption (900tpa). By contrast, actual UK consumption of AF paints accounts for only 30 tpa TBT with the rest being exported. Between 600 and 1100 tpa of TBT are consumed within the EC as a whole (in all applications).

Consultations indicated that TBT consumption was likely to decline as a result of a number of factors. Firstly, it was anticipated that consumption would fall over the next 5-10 years as a result of existing UK legislation (Environmental Protection Act, 1990) requiring improved controls on the disposal of tin containing wastes and discharges from dry dock repainting. Reduced consumption was also expected as a result of volun- tary moves within industry. For example, at the time, the Paintmakers Association of Great Britain was pressing for a withdrawal of free association TBT paints and a maximum TBT content of 1% in the copolymer formulations. It was anticipated that this would reduce TBT consumption by 20-30% and since the TBT case study was completed, these recom- mendations have, in fact, been adopted by the Advisory Committee on Pesticides (Health and Safety Executive, 1993). In addition, a number of ship operators had already made the move to tin-free paints as a result of "green" pressures and improvements in the efficacy of substitutes, and it was foreseen that this trend would continue.


Around 50% of the vessels which are permitted to use TBT-based paints actually do so when repainted in the UK. The main substitutes are those based on copper (cuprous oxide). Very few data exist on the efficacy of these substitutes due to the fact that they are new products which have not been around long enough for full in-service performance trials to have been completed. The RBA identified that the consensus within industry was that these substitutes are less efficient than TBT-based paints in the prevention of fouling (e.g. lifetimes of 30-48 months compared with 60 months for tin-based paints), but that efficacy is continually being improved. As a result of this and the fear of stricter regulation, it was considered that the remaining commercial life for TBT-based paints could be as short as 5 years.

As stated above, most of the data were derived from conversations with industry and, due to the lack of published data, it was not possible to clarify many of the figures provided. It is important to note, therefore, that the completeness and reliability of the data are uncertain.

Identification of life-cycle releases

There are no UK releases associated with the manufacture of TBT (the only EC-based production facilities being in the Netherlands and Germany). It was established that UK formulation activities take place within a controlled environment and are essentially a physical mixing and dispersion process as opposed to a chemical one; there are therefore few releases from these activities. The majority of TBT releases are associated with its use. Aquatic releases are those related to the application of AF paint to ships' hulls, the washdown or removal of paint from the hull surface and the leaching (by design) of TBT while in service. Aquatic releases dominate all releases, with only minor releases to the atmosphere (during application and grit blasting) and land (from the landfilling of TBT contaminated waters or grit blastings).

Environmental risk analysis

AF paints are designed to be toxic to specific forms of marine life. The concerns and risks associated with the use of TBT AF paints are that they have a detrimental effect on non-target organisms. There is an abundance of data which set out the effects of TBT on the aquatic environment and this was examined by the study team (few data exist pertaining to terrestrial or atmospheric releases, but, as the releases by these routes are limited, they were not considered to have significant environmental effects.


One factor which is important when considering the risks associated with a substance is the persistence of that substance and the reversibility of its effects. For TBT, permanent damage to species has occurred, and in some areas populat ions of specific species such as dog whelks have disap- peared. Data from the Ministry of Agriculture, Fisheries and Food ( M A F F ) indicated that where populations still exist, the effects of TBT are reversible if environmental concentrations are reduced (Waite e t al . ,

1991). The existence of TBT in sediment was identified as being important

when considering the effects o f a ban on TBT A F paints. When TBT is released into water, some (between 10 and 95%) is adsorbed onto particles which settle out and become incorporated into sediments and in addition, sediments (in the vicinity of marinas, etc.) contain paint chips. It is considered likely that following a ban on TBT A F paints, these sediments would continue to act as a "source" of TBT for some time to come as a result o f slow TBT degradation and dredging activities which may release TBT into the water column.

In an ideal world, equal consideration would have been given to the risks associated with TBT substitutes. This was not possible, however, as far fewer studies exist on the effects of copper-based A F paints. There is a need for more data and this was noted by the Advisory Committee on Pesticides in February 1993 (Health and Safety Executive, 1993). At the time of the study the available data indicated that copper was more desirable from an environmental viewpoint.

The study identified two techniques which could be used for the valuation of the environmental effects of TBT. The first was the market price technique, which can be used to value those effects which have some impact on the marketplace. Attempts were made to use this technique to value the increased oyster yields which would result from a ban on the use of TBT. To this end, M A F F data on shellfish landings were examined ( M A F F , 1974-1990). No clear trends were identified, however, and it was not possible to quantify the increases in oyster yields which would result from a complete ban on TBT 5. Had this been possible, then these increased yields would have been valued using the market price of shellfish (although the expected value of these increases would be small as the entire value of the U K oyster industry is only £2-3 million per annum).

The second technique which was identified was the contingent valuation

5The last year for which data were available was 1989, which was too early to indicate an increase in oyster yields as a result of the 1987 ban (on the use of TBT paints on vessels < 25m). It is also known that MAFF data are incomplete as not all landings are reported and because the statistics do not show farmed oysters.


method (CVM), which can be used to value those effects which have no impact on the marketplace. CVM is a social survey technique which attempts to value environmental goods by asking people for their will- ingness to pay (WTP) for some change in environmental quality. To value a ban on the use of TBT, a national survey could have been undertaken to determine people's W T P for a reversal in the effects of TBT. However, such surveys are expensive (in the region of £70,000) and take many months to complete. In addition, use of surveys for questions concerning conservation/preservation of the environment is still at an experimental stage. For these reasons, a survey was not undertaken as part of this study.

Human health risk analysis

In order to undertake the human health risk analysis, it was necessary to determine the effects of exposure to TBT and levels of exposure under the existing and proposed regulatory regimes.

Data on the effects of exposure are available from epidemiological studies and animal experiments. F rom the former it was possible to determine that direct contact with TBT results in dermatitis, and that aerosol inhalation results in acute irritation. Animal experiments provided information on the amount of TBT which would need to be consumed to initiate certain effects.

Very few data were available on levels of exposure. For workers, there have been no serious incidents to date, mainly as a result of good health and safety practices in dry docks. For the general public, the levels of exposure are unknown and this shortage of data on human exposure (either real or predictive) through food and water consumption, inhalation, etc., prevented full assessment of health risks. It is known that the risks to the general public must be low (and are probably minimal) for if TBT posed a greater risk then incidents would have occurred and been reported (consider Salmonella in eggs and Listeria in chilled foods, for example).

If TBT had been more harmful and exposure levels known, then it would have been possible to determine the number of people affected in terms of injuries and/or deaths. The impact on human health could then have been costed using a "value for a statistical life (or injury) ''6.

6In the UK, much of the work which has been undertaken to determine the "value of a statistical life" has been undertaken by the Department of Transport (DOT) for use in the evaluation of road proposals (see Dalvi (1988) for a review of estimates. The DoT assesses the merits of new roads partly by consideration of the numbers of lives which would be saved by them.


Economic assessment

Consideration was given to two levels of control, namely, the imposition of dock management controls for the collection of contaminated wash waters, and a total ban on the use of paints containing TBT. Two dockyard management controls were considered. These were dockyard management of waste and treatment of contaminated waste water 7. It was not possible to develop cost estimates for either. Costs relating to the dockyard management of wastes are mainly associated with the costs of disposal and these are highly site-specific (dependent on the distance between dockyard and landfill site, for example). Very few data exist on the costs associated with treatment. Although a range of treatment tech- nologies have been investigated, no method has been proven at full scale. One pilot plant was identified (in Portsmouth); however, it was not possible to obtain costings on which to base an assessment.

For a ban on the use of TBT, it was found that the impact would be increased costs, primarily to shipping and loss of income to dry docks. The costs can be broken down into four components. Firstly, there are increased paint costs as non-tin-based paints are around 20% more expensive. Secondly, because tin-free paints are less efficient, more fouling takes place and ships need to dry dock more often. Associated with this are the costs related to increased vessel "down time" (i.e. loss of earnings). Finally, as more fouling takes place, more fuel is used and fuel costs increase accordingly.

Discussions with ferry and tanker operators revealed that the break- down of costs was not the same for each type of operator. For ferries, almost all the costs of a ban were associated with increased paint costs, due to the fact that ferries are required to dry dock more often for safety reasons. For tanker operators, it was found that increased paint costs contributed around 9% to the total costs of a ban, and more frequent drydocking around 29%. The greatest cost component was loss of earnings at 62% and the smallest was increased fuel consumption at around 0.005%.

From these discussions it was estimated that the annual costs associated with a ban on the use of TBT would be between 50 pence and £ 1 per dead weight tonne (DWT). By using data on the dead weight tonnage of ships using U K and EC dry docks (for example, Marine Publications Interna- tional Ltd, 1992) it was possible to develop aggregate cost estimates of £10 million per annum (pa) for the U K and £135 million pa for the EC (1992 prices). There are also once-off costs associated with such a ban and these

7These were identified as ways of minimising releases of TBT to the marine environment by a separate study for Her Majesty's Inspectorate of Pollution (HMIP, 1992).


were estimated to be 60 pence per DWT resulting in costs of £6 million for the U K and £108 million for the EC. These costs are uncertain and open to question, but, because they are based on the actual experiences of operators who have changed to substitute paints, they are considered realistic.

While deriving these costs, it became clear that the major concern for dry dock operators was the potential employment effects associated with a ban on TBT use. It was felt that instead of changing to tin-free paints and using U K (or EC) facilities, shipping operators may choose to dock else- where (e.g. Eastern Europe, Asia). The potential effects were thought to be significant for an EC-wide ban due to the presence of the large dry docks in Spain and Portugal.

Evaluation of trade-offs

Through the above analysis, the trade-offs associated with a ban on the use of TBT-based paints were made explicit and these are set out below. It was found that such a ban would eliminate a key area of TBT use, but that the impacts on the U K alone would be small, as only 30 tpa of TBT is used in paints which are applied in the UK. Interestingly, even with no further controls on TBT it was felt that its use would decline as a result of "green image" considerations.

Under the existing control regime, TBT causes significant damage to shellfish and associated aquatic ecosystems. It was predicted that the amount of TBT in the environment (associated with existing use) would decline as a result of the proposed (now actual) withdrawal of free association paints from the marketplace. If TBT was banned, there would be recovery in the affected populations, although this would be delayed (due to the presence of TBT in sediments). TBT substitutes were considered to be less damaging to the aquatic environment. Finally, with respect to the terrestrial and atmospheric environments, the current usage of TBT AF paints was found to have no significant effects. As a result, a ban on TBT use would eliminate these impacts but would have no significant benefits.

The human health effects associated with the continued use of TBT AF paints are small. For workers, the potential effects are minimised through the adoption of good working practices and no serious incidents have been reported. The risks to the general public are unknown but are low and probably minimal. Thus, a TBT ban would have limited effects on human health; there would be a reduction in the potential effects on workers while the benefits to public health would be uncertain.

With or without a ban on the use of TBT, its remaining commercial life was considered to be limited (5-10 years at the most). The economic costs

Risk-benefit analysis and case study on tributyl tin 411

associated with a ban on the use of TBT were estimated to accrue to shipowners using dry docks and (when discounted at 6%) were found to be £50 million in the U K and £670 million in the EC over 5 years. In addition to these costs, it was felt that a ban would have potential employment effects with these being significant in other EC countries where larger dry dock are situated.

C O N C L U S I O N S

The Risk-Benefi t analysis approach was applied to decisions concerning the use of TBT in A F paints with some success. Although it was not possible to value the environmental and human health risks associated with its use, these were identified and were considered to be low for people and significant for the (aquatic) environment. The estimation of the economic costs o f a ban allowed the trade-offs associated with such a ban to be made explicit for the decision-maker. As a result, any decision on whether to ban TBT or not will be based (at least in part) on whether it is considered that the environmental and human health risks are worth more than £50 million (plus the potential loss of employment) over the next 5 years.

R E F E R E N C E S

Dalvi, M. Q. (1988). The Value o f Life and Safety: A Search for a Consensus Estimate. HMSO, London.

Department of the Environment (1991). Policy Appraisal and the Environment. HMSO, London.

HMIP (1992). Pollution control for antifouling paints/application in shipyards. Report No. DoE/HMIP/RR/047, Her Majesty's Inspectorate of Pollution, London.

HM Treasury (1991). Economic Appraisal in Central Government." A Technical Guide to Government Departments (commonly known as "The Green Book"), HMSO, London.

Haskoning (1989). Technical and economic aspects of measures to reduce water pollution caused by the discharge of TBT compounds. For the Commission of the European Communities, Directorate-General Environment, Consu- mer Protection and Nuclear Safety, Brussels.

Health and Safety Executive (1993). News Release E33:93, 23/2/93, Health and Safety Executive, Sheffield.

MAFF (1974-1990). Sea Fisheries Statistical Tables 1973-1989. HMSO, London (tables published annually).

Marine Painting Forum (1992). TBT Copolymer Anti-Fouling Paints: The Facts. Brochure published by the Organotin Environmental Programme Associa- tion (ORTEP) and the Marine Painting Forum, Tyne and Wear, July 1992.


Marine Publications International Ltd (1992). Drydock, Vol 14 Nos 1-3. Milne, A. (1990). Roughness and drag from the marine chemist's point of view.

Presented at the International Workshop on Marine Roughness and Drag, Royal Institution of Naval Architects, London, 29 September 1990.

Risk and Policy Analysts et al. (1992). Risk-Benefit Analysis of hazardous chemicals. Report prepared for the Department of the Environment, Contract No: 7/8/243, RPA, Norfolk, UK.

Waite, M. E. et al. (1991). Reductions in TBT concentrations in UK estuaries following legislation in 1986 and 1987. Marine Envir. Res., 32, 89-111.

risk-benefit analysis and case study on tributyl tin

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