Food Protection Trends - January/February 2018 - 23

TABLE 4. Estimate of number of standard servings of seafood required per day to exceed
the daily intake guidance values for Cu, Se and Zn
Age group/Body weight (kg)
Heavy Metal
Cu

Concentration

2-6 yrs/
19

7-12 yrs/
36

13-17 yrs/
62

18+ yrs/
78

2+ yrs/
70

Median (15.70 mg kg-1)

8.1

7.6

13.2

16.6

14.9

Max. (218.42 mg kg-1)

0.6

0.5

0.9

1.2

1.1

Median (0.49 mg kg )

6.5

6.1

10.5

13.3

11.9

Max. (4.1 mg kg-1)

0.8

0.7

1.3

1.6

1.4

-1

Median (230 mg kg )

1.1

1.0

1.8

2.3

2.0

Max. (1330 mg kg-1)

0.2

0.3

0.4

-1

Se
Zn

Note: A standard serving of seafood = 150 g day-1 and 75 g day-1 for adults and children (up to 6 yrs), respectively (11).
These serving sizes are equivalent to approximately 2 dozen (150 g of shellfish tissue) and 1 dozen (75 g of shellfish tissue) oysters.

Water (Fig. 1) during 2011. This prompted retesting of this
location during 2012, with findings of reduced concentrations of each metal (Cu: 16.96-28.14 mg kg-1, Se: 0.54-0.66
mg kg-1, Zn: 112.36-192.96 mg kg-1). These results may
have been due to increased sediment suspension caused by
strong winds and currents prior to sample collection, and
seasonal variability may have also contributed. All oysters
tested during this study were sampled directly from
the harvest area (i.e., no depuration) prior to analysis.
Depending on the harvest area classification, shellfish
stock may be subject to mandatory depuration prior to
sale. This process purges the particulate matter recently
filtered from the estuarine environment, which could
also contribute to elevated results.
The use of maximum reported concentrations in the
dietary exposure assessments was a conservative approach,
as the 90th and 99th percentile values were considerably
lower for Cu, Se and Zn (Table 2). Additionally, when
considering maximum concentrations, the lower number
of standard serves needed to exceed the recommended
dietary guidelines were due to the smaller body weight
of the age category groups below 18 yrs. Young children
generally tend to eat more food per kilogram of body weight
than older children or adults, and should be considered
separately in dietary exposure studies. However, these age
groups, particularly the 2-6 year age group, are unlikely to
eat large amounts of molluscs (2).
As well as being considered potential contaminants, Cu,
Se and Zn are also essential elements for correct human
physiological processes. Based on the current study, these
elements are not considered to be a risk to NSW shellfish

consumers. Toxicity from Cu is uncommon because of a
number of body systems that regulate Cu levels (9, 19).
While Hg does not appear to be a contamination issue in
NSW shellfish harvest areas, diets rich in Se can inhibit
methylmercury toxicity (24). Intoxication from Zn is
rare, and the negative harmful effects of excessive Zn
consumption appear to be from supplementary intake
rather than from naturally occurring Zn in food (10).
While heavy metals occur naturally in the environment,
anthropogenic influences from diffuse and point pollution
sources, run-off and stormwater from urbanized areas,
agricultural land use, mining and other catchment disturbances and atmospheric deposition can contribute to the
heavy metal load in estuarine settings (22). As filter feeders,
bivalve shellfish can accumulate potential contaminants
from their environment as suspended organic (food) and
inorganic particles as well as those dissolved in the surrounding solution (6, 23, 26). Illnesses related to metal
contamination in Australian seafood are extremely rare.
A recent risk assessment of the NSW Food Authority's
Seafood Safety Scheme (20) reported that the likelihood
of heavy metal contamination from seafood was low. There
are potential health concerns with mercury contamination
for certain groups, and pregnant and breastfeeding women,
women planning a pregnancy, and children up to 6 years to
are advised to avoid eating certain fish and to limit portion
sizes (20). From the available literature, this is the largest
survey of heavy metals in bivalve shellfish conducted along
the NSW coast of Australia, from the perspectives of both
time and geographic extent. Several studies have been
carried out on heavy metal concentrations in NSW shellfish

January/February Food Protection Trends

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