HEAVY METALS IN EDIBLE SEAWEEDS FROM COASTAL AREAS OF MANILA BAY AND ROXAS

Nancy Lazaro Llanos and Sean Mikhail B. Dalawampu. Chemistry Department, De La Salle University-Manila, 2401 Taft Ave. Manila 1004, Philippines. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History


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1430 markets along the Manila Bay area (Luzon). The samples were washed repeatedly with tap water and three times with distilled water. The samples were freeze-dried, grounded, and stored at -20ºC.
The cadmium, lead, and zinc content of the freeze-dried samples were subjected to acid digestion and analyzed via atomic absorption spectroscopy (Shimadzu AA-6300 model). All analysis was done in triplicate.

Identification of Seaweeds:-
The seaweeds were identified and authenticated by the Botany Division of the Philippine National Museum.

Results:-
The Cd, Pb, and Zn content in the freeze-dried seaweeds are summarized in Table 1. Results show that there is not much difference in the Cd content among the samples with values ranging from 0.1672 -0.2047 mg/kg. The amount of Pb is relatively lower in the C. racemosa samples collected from both locations (2.612 -2.709 mg/kg range). Pb content is significantly higher in the G. tenuistiptata sample collected during the month of June. Similar pattern as the Pb content was observed in the amount of Zn in the samples.

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A comparison of the average Cd, Pb, and Zn content (in mg/kg dry weight) are presented in Table 2. Results show the C. racemosa accumulated the least amount of heavy metal. Moreover, the Cd content is lower as compared to Pb in all the samples. Once more, data demonstrate that G. tenuistiptata accumulated a substantial amount of Zn as compared to the rest of the samples.  Data also show that Hypnea nidulans and Gracilaria tenuistipitata have a higher capacity to bioaccumulate Pb as compared to that of Caulerpa racemosa. It is noteworthy that Caulerpa species are a more popular ingredient in salads as compared to Hypnea and Gracilaria, however the latter are used as raw materials for making gelatin, thickening agents, and animal feed. Lenin Raj (2009) has presented data showing the relatively high capacity of a Hypnea species to accumulate heavy metals. Results are also consistent with the study of Mouradi et al. (2014) showing that the genus Gracilaria has a high ability to accumulate heavy metal. Gracilaria species is very common in the Manila Bay area, a highly urbanized area and relatively more polluted due to domestic and industrial wastes. This should explain the much higher concentrations of Pb and Zn. The amount of Zn between two batches of harvesting in Gracilaria is strikingly different. A possible explanation is that during the time of the second harvesting, there must have been a waste dumped in the Manila Bay area containing large amounts of Zn.
In France (CEVA, 2014), where seaweeds are considered as a novel food, the tolerable limit of Cd and Pb in dried seaweeds for human consumption has been set to 0.5 and 5 mg/kg dry weight, respectively. In the Philippines, the Food and Drug Administration has categorized dried seaweeds as processed food and has set a limit for adults of 0.3 and 10 mg/kg for Cd and Pb respectively. Therefore, based on these values, the amounts of Cd and Pb are generally still below the maximum limit. However caution must be considered with G. tenuistiptata which is a little above the limit set by France (CEVA, 2014).
The . Therefore results imply that generally, seaweeds, like marine products, can be a possible dietary source of Zn. Nevertheless, consumers must be aware of the Zn content in Gracilaria harvested from the Manila Bay area, which is beyond the limit set by FAO/WHO.

Conclusion:-
This study has shown that values of Cd, Pb, and Zn in Caulerpa racemosa, a popular ingredient used in seafood salads, is well below the limit indicating very little risk posed by consumption of this seaweed. Although, still below the limit, consumers must be aware of the relatively higher heavy metal content in Hypnea. Moreover, consumption of Gracilaria is of main concern, considering that among the three species, it is the one with the highest heavy metal content. Regular monitoring is necessary to protect consumers from deleterious effects of seaweeds consumption.