Food Protection Trends - January/February 2018 - 19

to the protection of shellfish consumers. This paper
presents the most comprehensive study to date of potential
contaminants (inorganic arsenic (As), cadmium (Cd),
copper (Cu), lead (Pb), mercury (Hg), selenium (Se)
and zinc (Zn)) in aquaculture zones across 2,000 km of
the New South Wales (NSW) coastline (Fig. 1) between
1999 and 2014. There is no decisive definition for 'heavy
metals'; they are broadly classified as elements that have
a specific density > 5 g cm-3 (28). Metalloid substances
such as As are often grouped with heavy metals on the
basis of the interchangeable association between heavy
metals and environmental toxicity (8, 15, 28). While Se
is a non-metal, it can be toxic at high concentrations (1).
Of the chemicals tested, only inorganic As, Cd, Pb and Hg
have maximum limits (MLs) mandated for bivalve molluscs
within the Australia New Zealand Food Standards Code
(FSC) ((12), Table 1). Cu, Se and Zn are considered as
essential micronutrients as well as potential contaminants.
Internationally accepted dietary guidelines (Table 1) were
used to determine whether concentrations of these three
elements represented a risk to shellfish consumers.
MATERIALS AND METHODS
Shellfish samples were collected from commercial aquaculture areas every three years between 1999 and 2014 from

up to 31 estuaries along the coast of NSW, Australia (Fig.
1), as part of an ongoing monitoring program (4). Samples were representative of the main species harvested in
each estuary. This was predominantly Sydney rock oysters
(Saccostrea glomerata), along with some Pacific oysters
(Crassostrea gigas), blue mussels (Mytilus edulis) and
cockles (mainly Anadara trapezia and Katelysia spp.), where
available. Oyster cultivation is predominantly in intertidal
racks in plastic trays, baskets or containers, with relatively
little stick culture. Mussel cultivation is via long lines. Marketable size shellfish were selected where possible. Within
each harvest area, samples were collected from upstream
and downstream locations and at various distances from
the shoreline. Samples were pooled to provide 150-200 g
of tissue (approx. 20-30 shellfish). Not all locations were
sampled at every round, because of the prevailing operational status of the harvest area and time constraints. Samples from each estuary were shucked, bottled, labelled and
frozen (-20°C) at the NSW Food Authority before being
transported to National Association of Testing Authorities,
Australia (NATA) accredited laboratories for analysis.
All samples were screened for Cd, Cu, Pb, Hg, Se and Zn.
In 2002, inorganic As was added to the suite of analyses.
In seafood, inorganic As is ~10% of total As (27, 30).
A recent analysis of Australian seafood by Stewart and

FIGURE 1. Estuaries and embayments that host currently classified shellfish aquaculture areas in New South Wales, Australia.

January/February Food Protection Trends

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