Catherine McLeod

Paralytic shellfish toxins (PST) were identified in the hepatopancreas of Southern Rock Lobster (Jasus edwardsii) during Alexandrium tamarense blooms in Tasmania, Australia. Human health risk from PST in lobsters was unknown – this study assesses exposure to PST from hepatopancreas consumption. Lobster hepatopancreas samples collected during blooms (n = 181) were mostly positive for PST (>88%), the highest concentration was 4032 μg STX-2HCl eq/kg. Consumer exposure to PST was estimated using a 2-D Monte Carlo model. Mean PST intake (pi) from hepatopancreas consumption (raw and cooked) was below the lowest-observed-adverse-effect-level (LOAEL) for PST (pi for raw meals (2.64 μg/kg bw) exceeded the LOAEL. A total of 4.1% of raw hepatopancreas meals were estimated to exceed the LOAEL. Lobster hepatopancreas consumption during A. tamarense blooms may be concerning for a small proportion of consumers, particularly those that eat large meals at the bloom peak. However, when the model was re-run with PST concentration capped at the bivalve regulatory limit (800 μg STX-2HCl eq/kg) pi decreased, with the 97.5th percentile values below the LOAEL. Thus, issuing public health warnings and harvesting restrictions for lobsters when levels exceed 800 μg STX-2HCl eq/kg would reduce the probability of illness occurring.

In 2012 and 2015, blooms of Alexandrium tamarense occurred in Tasmania, Australia, and paralytic shellfish toxins (PST) were identified in the hepatopancreas of Southern Rock Lobsters. The human health risk was unclear, because consumption data were not available for lobster hepatopancreas. Thus, the aim of this study was to investigate the types of lobster tissues consumed, hepatopancreas portion size, and consumption format (boiled, steamed, raw, etc.), for Tasmanian and South Australian recreational harvesters. A significant proportion of harvesters (15%) eat lobster hepatopancreas, with the majority consuming it as a dipping sauce for cooked (boiled or steamed) lobster meat. Two different methods were used to estimate portion size, a recollection-based food consumption questionnaire (FCQ) and a prospective Food Diary – mean portion size estimates showed good agreement: 3.4 g and 4.8 g, respectively. These results are critical for assessing the exposure of recreational harvesters to acute contaminants, such as PST, in lobster hepatopancreas. Results from the FCQ showed that lobster hepatopancreas is not consumed as often as white meat, suggesting that exposure to contaminants in hepatopancreas may be less frequent than white meat. This should be considered when evaluating human health risk from repeated or long term (chronic) exposure to contaminants in lobsters.

This paper reports a study of norovirus (NoV) GII distribution and persistence in Sydney rock oysters (SRO) (Saccostrea glomerata) located in an estuary after a pump station sewage overflow. SRO were strategically placed at six sites spanning the length of the estuary from the pump station to the sea. The spatial and temporal distribution of NoV, hepatitis A virus (HAV) and Escherichia coli (E. coli) in oysters was mapped after the contamination event. NoV GI and GII, HAV and E. coli were quantified for up to 48 days in oysters placed at six sites ranging from 0.05 to 8.20 km from the sewage overflow. NoV GII was detected up to 5.29 km downstream and persisted in oysters for 42 days at the site closest to the overflow. NoV GII concentrations decreased significantly over time; a reduction rate of 8.5% per day was observed in oysters (p < 0.001). NoV GII concentrations decreased significantly as a function of distance at a rate of 5.8% per km (p < 0.001) and the decline in E. coli concentration with distance was 20.1% per km (p < 0.001). HAV and NoV GI were not detected. A comparison of NoV GII reduction rates from oysters over time, as observed in this study and other published research, collectively suggest that GII reduction rates from oysters may be broadly similar, regardless of environmental conditions, oyster species and genotype.

Pollution of coastal waters can result in contamination of bivalve shellfish with human enteric viruses, including norovirus (NoV), and oysters are commonly implicated in outbreaks. Depuration is a postharvest treatment involving placement of shellfish in tanks of clean seawater to reduce contaminant levels; this review focuses on the efficacy of depuration in reducing NoV in oysters. There have been many NoV outbreaks from depurated oysters containing around 10 ³ genome copies/g oyster tissue, far exceeding the median infectious dose (ID50). Half of the published NoV reduction experiments showed no decrease in NoV during depuration, and in the remaining studies it took between 9 and 45.5 d for a 1‐log reduction—significantly longer than commercial depuration time frames. Surrogate viruses are more rapidly depurated than NoV; the mean number of days to reduce NoV by 1 log is 19, and 7.5 d for surrogates. Thus, surrogates do not appear to be suitable for assessing virological safety of depurated oysters; data on reduction of NoV infectivity during depuration would assist evaluations on surrogate viruses and the impact of methods used. The longer persistence of NoV highlights its special relationship with oysters, which involves the binding of NoV to histo‐blood group‐like ligands in various tissues. Given the persistence of NoV and on‐going outbreaks, depuration as currently performed appears ineffective in guaranteeing virologically safe oysters. Conversely, relaying oysters for 4 wk is more successful, with low NoV concentrations and no illnesses associated with products. The ineffectiveness of depuration emphasizes the need for coastal water quality to be improved to ensure oysters are safe to eat.

The first national survey of Australian wild-caught abalone was conducted between September 2012 and December 2013. The aim of the survey was to determine the presence of paralytic shellfish toxins (PSTs), amnesic shellfish toxins (ASTs), and diarrhetic shellfish toxins (DSTs) in wild-caught abalone at levels above the current Codex marine biotoxin limits during the 2013 fishing season. Abalone (n = 190) were collected from 68 abalone-fishing blocks for which the combined annual harvest accounts for 80 % of Australian production. Concurrent seawater samples were collected and enumerated for potentially toxic phytoplankton. The foot and viscera tissues of each abalone sample were analyzed separately for PSTs, ASTs, and DSTs. No samples (abalone foot or viscera) contained toxins at levels exceeding the marine biotoxin limits stipulated by Codex. The resulting prevalence estimate suggests that less than 1.6 % of the commercially caught wild abalone population in Australia were contaminated with marine biotoxins at levels above the regulatory limit during the survey period. ASTs were detected at very low (trace) levels in the foot and viscera tissue of four and three abalone samples, respectively. To our knowledge, this represents the first reported detection of domoic acid in Australian abalone. PSTs also were detected at very low levels in 17 samples of abalone foot tissue and 6 samples of abalone viscera. The association between the low levels of ASTs and PSTs detected in abalone and the presence of potential toxin-producing phytoplankton in seawater samples was weak. DSTs were not detected in any abalone despite the detection of very low levels of DST-producing phytoplankton in a small number (9 of 77) of seawater samples. The results of this survey should be useful for public health risk assessments and provide additional evidence that the prevalence of marine biotoxins in Australian wild-caught abalone is very low.