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Archives
Aug 1-31, 2003
Detecting chemical
contaminants in canned tuna and rice
by Likha C. Cuevas
We have lead and cadmium in our food?
 Yes,
and our food like the canned tuna that we export and
rice must be analyzed to determine if they contain these
contaminants. Dr. Evangeline C. Santiago of the Natural
Sciences Research Institute (NSRI) at the University
of the Philippines Diliman (UPD) discussed this topic
in the seminar on, "Identification and Initial
Validation of an Analytical Method for the Determination
of Lead and Cadmium in Fish (Canned Tuna) and Rice Samples
to be used for Monitoring and Regulatory Purposes,"
on August 6, 2003 at the Bureau of Agricultural Research
(BAR) CERDAF Conference Room. This seminar has been
organized by the Product Quality Systems Network (PQSN)
and co-sponsored by BAR.
According to Dr. Santiago, cadmium and
lead are metals with no known role in metabolism but
have been involved in historic poisoning episodes of
human populations and wildlife resulting from contaminated
food and prey. They are introduced to the environment
by human activities usually from mining and metal industries
and from leaded gasoline. These metals that are released
into the atmosphere, may settle with dust particles
on plants and crops or may find their way to the soil
and coastal and river waters and sediments.
Cadmium may be present in big amounts
in soil fertilized with sewage sludge. The toxicity
of cadmium includes the direct binding of this contaminant
with the negative groups of DNA to produce precursors
of tumors. Lead, on the other hand, is deposited on
and retained by crops, particularly leafy vegetables
and fruits. Fish are contaminated by lead that ranges
from 0.1 ppm and up to 0.8 ppm for shellfish. Canned
goods are also contaminated through leaching of lead
solder in cans while others get contaminated from lead
glazes in pottery and ceramic ware.
Lead accumulates in the body over a lifetime
and the body releases it slowly. Over time, even in
small doses, this can cause lead poisoning with impairment
of the nervous system as one of its effects. To prevent
these from happening to consumers, monitoring contaminants
in food for trade and regulatory purposes has to satisfy
the criteria for data quality set by CODEX. CODEX specifies
a set of criteria for acceptability of the method in
analyzing a specific contaminant in a particular matrix.
The study that Santiago and her team
of experts regarding lead and cadmium contamination
analysis validated an analytical method that meets the
CODEX criteria for analysis of lead in fish and cadmium
in rice in three selected local laboratories under a
supervised inter-laboratory analysis program. The supervised
laboratory program then used a set of documented test
procedures and test materials to eliminate as much variability
between laboratories.
The study showed that the analysis of
cadmium in rice using the standard AOAC procedure involving
dry ashing and direct aspiration in Atomic Absorption
Spectrophotometry (AAS) for monitoring and regulatory
purposes can be done at the Institute of Chemistry (IC)
at the UP Los Baños (UPLB), Philippine Institute
of Pure and Applied Chemistry (PIPAC) in Ateneo de Manila
University, and the Research and Analytical Services
Laboratory (RASL) of NSRI. The research team, however,
concluded that the analysis of lead in canned fish in
these local laboratories using standard AOAC method
does not satisfy the requirements of CODEX/EU for the
detection limits and precision of the analytical method
for the specified regulation level of 0.5 mg/kg lead.
Santiago said, "the laboratory at
NSRI showed that modification of the method by chelation
(the process of forming a ring with one or more hydrogen
bonds with the use of organic chemical that bonds with
and removes free metal ions from solutions) of the digests
before AAS analysis can satisfy the requirements on
the detection limit and precision. Full validation of
the modified method is recommended before it can be
used to analyze lead in tuna."
The full validation of the modified method
is recommended before it can be used to analyze lead
in tuna. "Since AAS is a common instrument and
is available in laboratories, BFAR is already training
their analysts on this method," Santiago added.
There is no reference laboratory yet for this method.
Can local laboratories comply with the
requirements for trade exports? For the meantime, Santiago
explained, local laboratories are using the AOAC method.
Their methods will not be acceptable (in international
standards) since unspiked tuna samples analyzed would
have no lead detected because AOAC has a low method
detection level.
Tuna industries do not support the analysis
of lead and instead proposed the removal of the regulation
level. This cannot be done, however, since it is a requirement
in international trade, Santiago said. Since CODEX wanted
to lower the regulation level of lead in tuna (2 ppm
for trace metals), the formation of a reference laboratory
for trade export is subject to the technical capabilities
of analysts. 
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Detecting chemical contaminants in canned tuna and rice
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