Appendix 5
Background: Requirements for producers of bivalve molluscs
The draft Standard in the Draft Assessment Report for Proposal P265 (Development of a Primary Production and Processing Standard for Seafood) included a definition for ‘bivalve molluscs’ which specifically excluded ‘spat, scallops and pearl oysters where the only part of the product consumed is the adductor muscle’.
The implication of this definition was that producers of roe-off scallops and pearl oyster meat (spat are juvenile molluscs andare not normally eaten) were excluded from having to comply with Division 3 of the Standard, while producers of all other bivalves were required to meet those requirements.
Several submissions to FSANZ did not support excluding pearl meat producers from having to comply with the Division 3 requirements of the draft Standard, and two sought confirmation that there was sufficient scientific justification for the exclusion. Two submissions supported the exclusion.
In addition, the potentially onerous effect of the requirement for classification of harvest waters under Division 3 of the draft Standard on the wild oyster and offshore scallop industries was raised in submissions and in consultations. It is understood that the roe-on component is a small but expanding portion of the offshore scallop industry. The Division 3 requirement would not apply to the roe-off component of the industry.
The supply of pearl oyster meat is likely to increase in future years, as the feasibility of pearl oyster aquaculture in estuarine environments is being investigated in Australia. In NSW, for example, a small industry is being developed in Port Stephens and other estuaries.
If estuarine pearl producers were wishing to market pearl oyster meat as a by-product, the food safety implications would need to be separately considered, as the range of associated food safety hazards might be different. The producers have been advised by the NSW Food Authority that any pearl meat marketed would have to be produced under the requirements of the NSW Shellfish Program.
Consideration is also being given to use of pearl oyster aquaculture as a means of bioremediation of polluted waterways (Gifford et al., 2004), although it must be assumed that the meat would not be marketed from these animals. It should be noted, however, that the considerations below apply only to pearl oyster meat from offshore, remote locations
The global public health and economic impacts of algal biotoxins, the likelihood of those impacts increasing in scale as aquaculture expands, and the vulnerability of the Australian shellfish industry were highlighted in a recent report to the Australian Shellfish Quality Assurance Advisory Committee (Cawthron Institute, 2001).
Scientific issues
Introduction
The hazards of concern with pearl oyster meat and offshore scallops are algal biotoxins. Hazards derived from faecal pollution and agricultural run-offs, such as enteric bacterial and viral pathogens, are not currently a significant issue because harvesting currently occurs at relatively remote offshore locations. It is generally recognised that very little toxin migrates from the viscera into the adductor muscle in scallops.
Public health data
There is no evidence of illness from algal biotoxins in scallops or pearl oysters in Australian epidemiological datasets. Unfortunately, outbreak datasets are usually incomplete and capture information on only a fraction of the total food-borne illness in Australia. Furthermore, sporadic cases of food-borne illness (where illness is scattered; occurring singly and not as an outbreak) are not included in these datasets (unless a death results and the food vehicle is identified). Low levels of reporting, even of quite severe food-borne illnesses, are a major data gap and introduce uncertainty into the scientific evaluation. For this reason, FSANZ does not rely solely on outbreak data in evaluating the public health risks due to food safety hazards.
Accumulation of toxins in bivalves
There are no reports in the scientific literature relating to prevalence, concentration or distribution of algal biotoxins in pearl oysters (Pinctada spp.). A proposed study on the accumulation of algal toxins in pearl oyster meat by the pearl oyster industry has yet to get underway.
Given the large inter-species variation in the ability of bivalves to accumulate and detoxify algal biotoxins (see, for example, Bricelj and Shumway, 1998), it is not sound to extrapolate from the findings of low accumulation in scallop adductor to assume a similar low level of accumulation in pearl oyster meat. Assumptions made about toxin uptake being similar between different species might turn out to be incorrect once data is available.
There is evidence that bivalves harvested from areas of fast currents and/or deep waters are still able to accumulate toxins. Paralytic shellfish poisoning (PSP) toxin has been found at high levels in sea scallops (Placopecten magellanicus) harvested at a depth of 180 metres in the Gulf of Maine, USA (Cembella et al., 1993), and from areas subject to 14 metre tidal flows in the Bay of Fundy, Canada (Watson-Wright et al., 1990).
Campbell et al. (2001) report that in king scallop (Pecten maximus) samples taken from a closed harvest area in north west Scotland, the level of algal biotoxin (ASP) accumulating in adductor muscle was very low, and they did not find levels exceeding the regulatory limit. However, while the level of toxin in roe was much lower than in other tissues (except adductor muscle), 22% of individual roe samples still exceeded the regulatory limit (20 mg/kg).
New Zealand applies a scheme of flesh testing of scallops from its commercial scallop fisheries (including offshore-remote fisheries). Roe samples are tested (usually weekly) for the four major classes of algal biotoxins, and ‘muscle & roe’ samples are tested if the roe toxin level exceeds a trigger level65. Combined results from ten years of commercial and non-commercial testing programmes have been recently reviewed (NZFSA, 2003). Some samples of scallop roe and ‘muscle & roe’ were found to have levels of ASP higher than the maximum limit allowed in the Code.
Summary of scientific issues
FSANZ concludes that there is significant variability in interspecies accumulation of algal biotoxins such that it is not appropriate to extrapolate from scallops to pearl oysters, given the severity of the health impact of algal biotoxins and the absence of specific data from Pinctada species.
Although scallop adductor muscle does not accumulate significant levels of algal biotoxins, available data implies that the roe may accumulate toxins to levels that might pose a significant public health and safety risk following consumption of roe-on scallops sourced from offshore harvest areas.
Applying the Risk Ranking Methodology
In completing the Risk Ranking of Seafood in Australia, FSANZ did not apply the ranking matrix to individual species of seafood or to very small fisheries such as pearl oyster meat. The consequences of the very low per capita consumption of such products inevitably drives the likelihood rating to ‘unlikely’.
Commodity
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Hazard/environment
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Severity
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Likelihood
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Relative risk ranking1
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Current risk management
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Pearl oysters meat
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Algal biotoxins (ASP, PSP)
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Severe
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Unlikely
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Medium
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1. Risk ranking reflects current practice for that commodity/seafood sector. The risk ranking is based on the severity of the hazard and an estimate of the likelihood of illness that takes into account various factors, including current risk management practices.
2. Current risk management involves maximum level standards for the four major classes of algal toxins in the Food Standards Code.
Given the relatively small size of the industry, anecdotally of the order of 5-10 tonnes per year, there is only a very low level of consumption of pearl oyster meat when considered across the whole Australian population. The likelihood of illness rating for the whole population is thus ‘unlikely’ and the risk ranking is ‘Medium’.
There are a number of sources of uncertainty impacting upon this risk ranking. The critical uncertainty surrounds the fate of any toxin ingested by the oyster. There are no data specific to pearl oysters, and extrapolation from data relating to distantly-related bivalves such as scallops was considered unsound given the large inter-species variation in the ability of bivalves to accumulate and detoxify algal biotoxins. Other sources of uncertainty include the size of the consuming population and the likelihood of toxic algae being present in the harvest waters. These sources of uncertainty affect the ‘likelihood of illness’ rating in the risk ranking.
The risk ranking model is difficult to apply in situations of such high uncertainty. The uncertainty regarding the presence of algal toxin in pearl oyster meat means that if the risk ranking was applied to the subset of the population that consumes the product, the likelihood of illness rating could range from unlikely to likely, and this would impact on the final risk ranking. Specific data on the bioaccumulation of biotoxins in pearl oysters would resolve the uncertainty in the ranking.
References
Bricelj, V.M. and Shumway, S.E. (1998) Paralytic shellfish toxins in bivalve molluscs: occurrence, transfer kinetics, and biotransformation. Rev. Fisheries Sci. 6(4): 315-383.
Campbell, D.A., Kelly, M.S., Busman, M., Bolch, C.J., Wiggins, E., Moeller, P.D.R., Morton, S.L., Hess, P. and Shumway, S.E. (2001) Amnesic shellfish poisoning in the king scallop, Pecten maximus, from the west coast of Scotland. J. Shellfish Res. 20(1): 75-84.
Cawthron Institute (2001) Australian biotoxin management plan for shellfish farming. An FRDC-funded project for the Australian Shellfish Quality Assurance Advisory Committee. Cawthron Institute, Nelson, New Zealand.
Cembella, A.D., Shumway, S. E. and Lewis, N.I. (1993) Anatomical distribution and spatiotemporal variation in paralytic shellfish toxin composition in two bivalve species from the Gulf of Maine. J. Shellfish Res. 12: 389–403.
Gifford, S., Dunstan, R.H., O’Connor, W., Roberts, Y. & Toia, R. (2004) Pearl aquaculture – profitable environmental remediation? Sci. Total Environ. 319(1-3): 27-37.
NZFSA (2003) Non-commercial marine biotoxin monitoring in New Zealand: risk-based programme enhancement – final report, May 2003. New Zealand Food Safety Authority. http://www.nzfsa.govt.nz/animalproducts/publications/reports/biotoxin-report.pdf. Accessed on 22 November 2004.
Watson-Wright, W., Richard, D., Belliveau, A., McGuire, A. and Marshall, I. (1990) PSP content of roe cannot be predicted from that in other tissues of Bay of Fundy scallops (Placopecten magellanicus) Toxicon 28(6): 628. (Conference Abstract: Third Pan. Amer. Symp. on Plant, Animal and Microbial Toxins, Oaxtepec, Mexico, 1989).
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