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American Journal of  
Life Science and Innovation (AJLSI)

Heavy Metal Analysis in Crassostrea iredaleiCrassostrea iredalei (Slipper Oyster) from Dumangas and Barotac 
Nuevo, Iloilo, Philippines

Carisma G. M. S.1, Campania N. F.1, Casipe B. J.1, Chua A. D. T.1, Consolacion J. R. I.1, Daylo D. K. S.1, Dela Cruz A. P. J.1, 
Escultero H. J. R.1, Fajardo O. M. G.1, Falsis H. I. D.1, Felecio J. R. B.1, Blancaflor J. M.1, Palmos R. J. P.1, Visitacion R.1, Leong-on M. S.1*

Volume 4 Issue 2, Year 2025
ISSN: 2833-1397 (Online)

DOI: https://doi.org/10.54536/ajlsi.v4i2.5047
https://journals.e-palli.com/home/index.php/ajlsi

Article Information ABSTRACT

Received: April 20, 2025

Accepted: May 22, 2025

Published: October 11, 2025

It is relevant to analyze the concentrations of  heavy metals in C. iredalei. This study was 
conducted to analyze the concentrations of  the heavy metal contents, such as copper (Cu), 
lead (Pb), and zinc (Zn) in C. iredalei from Dumangas and Barotac Nuevo, Iloilo, Philippines. 
The samples of  C. iredalei were analyzed using flame atomic spectrophotometry, and results 
were compared to regulatory limits set by the International Shellfish Safety and Sanitation 
Standards. In the town of  Dumangas, Pb (mean = 0.01mg/L; sd = 0.11;) Cu (10.44 mg/L; 
sd = 2.95); and Zn (mean = 3.35 mg/L; sd = 0.13) were within the accepted values set by the 
regulatory limits of  the International Shellfish Safety and Sanitation Standard. The samples 
of  C. iredalei were taken from March 31st and April 7th, 2023. On the other hand, in the 
town of  Barotac Nuevo, Pb (mean = -0.09, mg/L s = 0.02); Cu (mean = 10.14 mg/L, sd = 
0.95; and Zn (mean = 3.21 mg/L; sd = 0.10) were within were within the accepted values 
set by the regulatory limits of  the International Shellfish Safety and Sanitation Standard, too. 
This implies that the C. iredalei samples from farms in towns Dumangas and Barotac, Iloilo, 
Philippines, were safe for consumption and do not pose threats concerning heavy metal 
intoxication.

Keywords

Crassostrea Iredalei, Heavy Metal 
Determination, Slipper Oyster, 
Spectrophotometry

1 College of  Pharmacy and Medical Technology, University of  San Agustin, Iloilo City, Philippines
* Corresponding author’s e-mail: mleongon@usa.edu.ph

INTRODUCTION 
A popular delicacy that is widely cultivated in the 
Philippines for human consumption is the slipper oyster, 
or Crassostrea iredalei (Monaya et al., 2022). Therefore, 
encouraging a sustainable economy will raise the fishing 
industry’s and its related sectors’ economic value (Rustia 
et al., 2023). It is a popular item throughout Asia due to its 
inexpensive cost, especially among the poor (Pakingking 
et al., 2022). One essential food source that may be found 
all across the coastal region is C. iredalei. The nation 
produced 40,736.89 metric tons (MT) of  C in 2021. 
Western Visayas contributed 10,886.16 MT, the second-
highest amount among the other regions (Department of  
Agriculture’s Bureau of  Fisheries and Aquatic Resources, 
2022).
Meat production for domestic use is the primary 
objective of  oyster farming. By 2020, it is anticipated that 
oyster production alone will be worth Php 1.552 billion. 
Nutrition, food security, and the battle against poverty 
depend on them because they are the primary source of  
food and money for poor fishermen (Lebata-Romos et 
al., 2023). Situated in the center of  the Philippines, the 
Western Visayas region is one of  the main suppliers of  
oysters. More farms are being established in the Western 
Visayas region as a result of  the need for extra sources of  
income brought on by small-scale fishermen’s diminishing 
catch.
However, contamination in aquatic biological systems 
has become much more common in recent years due to 
mining and agricultural activities (Noman et al., 2022). 
Heavy metals in coastal and estuarine ecosystems, 

along with other environmental pollutants, have raised 
concerns in environmental conservation (Wang et al., 
2022). Oysters are filter feeders that can collect pathogens 
from surrounding waters, potentially causing foodborne 
diseases in consumers (Pakingking et al., 2022). 
Persistently polluted organisms absorb heavy metals, 
which can cause severe illnesses such food poisoning, 
liver damage, cardiovascular abnormalities, and even 
death (Anandkumar et al., 2018). Food contamination by 
toxic heavy metals is a worldwide environmental risk that 
impacts hundreds of  millions of  people. Their toxicity 
results in a broad range of  harmful biological effects 
(Balali-Mood et al., 2021). Oysters are valued as delicacy, 
but their fitness for human consumption should be 
monitored, especially as they are believed to be hyper-
accumulators of  a number of  dangerous metals, such as 
cadmium, copper, and zinc (Wang & Weng, 2018). Cellular 
processes such as growth, proliferation, differentiation, 
damage repair, and apoptosis are all hampered by heavy 
metals. Through the production of  Reactive Oxygen 
Species (ROS), oxidative stress, enzyme inactivation, and 
weakened antioxidant defense, these metals cause toxicity.  
High levels of  exposure to heavy metals, especially lead 
and mercury, can cause serious side effects such as kidney 
failure, bloody diarrhea, and colic in the abdomen (Tsai 
et al., 2017).
Due to equipment problems, the Bureau of  Fisheries 
and Aquatic Resources (BFAR) has not performed heavy 
metal analyses in the past four years, saving them for cases 
of  oyster exportation outside of  the country (R. Chua, 
personal communication, January 10, 2024). Therefore, it 



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Am. J. Life Sci. Innov. 4(2) 11-14, 2025

seems sense to investigate the levels of  heavy metals in C. 
iredalei in Dumangas and Barotac Nuevo, Iloilo.
The purpose of  this study was to examine the levels 
of  heavy metals in C. iredalei from Barotac Nuevo and 
Dumangas, Iloilo. In particular, this study was able to 
characterize the many types of  heavy metals that are 
present in C, including lead (Pb), copper (Cu), and zinc 
(Zn). C iredalei, from the oyster farms at Barotac Nuevo 
and Dumangas, Iloilo, during the last week of  March and 
first week of  April 2024. Additionally, the study measured 
the amounts of  Cu, Pb, and Zn in C. iredalei at the time of  
collection and determined the heavy metal concentration 
in C. iredalei with regard to the International Safety and 
Sanitation Standard for Shellfish.
According to the study’s findings, it was safe to eat C. 
iredalei from the municipalities of  Dumangas and Barotac 
Nuevo. In the last week of  March and the first week 
of  April 2024. The Pb, Cu, and Zn levels were within 
the permissible range established by the International 
Shellfish Safety and Sanitation Standards.

MATERIALS AND METHODS
Research Design
The occurrence of  heavy metals like lead (Pb), copper 
(Cu), and zinc (Zn) in oysters from Dumangas and 
Barotac Nuevo, Iloilo, was investigated using a descriptive 
quantitative design. Additionally, it determined that the 
concentrations of  certain heavy metals were within 
permissible bounds.

Research Setting
Oyster farms in Dumangas and Barotac Nuevo provided 
the data for this investigation. The laboratory of  a private 
institution in Iloilo City was used to examine the heavy 
metals.

Ethical Considerations
This study was approved by the ethics committee of  a 
private university in Iloilo City.

Data Collection Procedures
Collection of  C. iredalei: For two weeks, C. iredalei samples 
were taken every week from two locations: Dumangas 
and Barotac Nuevo.
Preparation of  Samples: In accordance with the techniques 
of  Azevedo et al. (2019), Pakingking et al. (2022), and 
Villafuerte et al. (2022), the C. iredalei were taken out of  
their shells using a knife. During transportation, the meat 
and intravenous fluid were gathered in a zippered storage 
bag and kept on ice. A mortar and pestle were then used 

to defrost and homogenize the samples. After being 
moved to their individual crucibles, the homogenates 
were weighed at 25 grams apiece.
After being dried at 105 °C in a Memmert Drying Oven, 
the oyster samples were moved to a muffle furnace and 
heated for at least 24 hours at an increasing temperature 
of  450 °C to 500 °C. A desiccator was then used to chill 
the samples. Two milliliters of  nitric acid were added to 
each oyster sample, which was then heated on a hot plate 
until it dried. To get carbon-free ash, this process was 
carried out at least twice.
The samples were cooked on a hot plate with ten milliliters 
of  1N hydrochloric acid until all of  the ashes had been 
dissolved. Following a 2.5 millimeter pore size Whatman 
Grade 5 filter, the materials were moved to a 25 milliliter 
volumetric flask.
Detection of  Heavy Metals: A flame atomic absorption 
spectrophotometer (Agilent AA55 MY1546001) was used 
to measure the levels of  Cu, Pb, and Zn in the filtered 
digests. The stock standard solution was diluted to a 
concentration of  1000 micrograms per milliliter (µg/mL) 
or parts per million (ppm) in order to create all of  the heavy 
metal standard solutions. The stock solution was then 
further diluted into concentrations of  0.300, 0.500, 0.700, 
1.000, and 1.500 µg/mL to create the working standard 
solutions. Every result was expressed in parts per million 
or milligrams per liter. Analytical grade substances were 
used in this investigation. A certified chemist examined 
and verified the study. Five (5) replicates of  each of  the 
two (2) sets of  samples were examined.
Interpretation of  Results: The mean and standard 
deviation were used to determine whether the results 
fell within the range of  the International Shellfish Safety 
and Sanitation Standards, which are regulatory limits 
established by the Food and Drug Administration and 
the European Union.

RESULTS AND DISCUSSIONS
The results showed that the Zn (mean = 3.35 mg/L; sd = 
0.13), Cu (mean=10.44 mg/L; sd = 2.95), and Pb (mean = 
0.01 mg/L; sd = 0.11;) in the municipality of  Dumangas 
were all within the acceptable levels established by the 
International Shellfish Safety and Sanitation Standard 
(Table 1). The C. iredalei samples were taken from March 
31 and April 7, 2023. On the other hand, Pb (mean = -0.09 
mg/L, s=0.02), Cu (mean = 10.14 mg/L, sd = 0.95), and 
Zn (mean = 3.21 mg/L, sd = 0.10) were all within the 
permitted limits established by the International Shellfish 
Safety and Sanitation Standard in the town of  Barotac 
Nuevo.

Table 1: Concentrations of  Heavy Metals in C. iredalei Collected from Dumangas, Iloilo, Philippines
Heavy Metal Accepted Value Concentration (mg/L) Mean SD Interpretation
Pb 1.5 0.01 0.12 Within accepted values
Cu 100 10.44 3.23 Within accepted values
Zn 150 3.35 0.14 Within accepted values



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Table 2: Concentrations of  Heavy Metals in C. iredalei Collected from Barotac Nuevo, Iloilo, Philippines
Heavy Metal Accepted Value Concentration (mg/L) Mean SD Interpretation
Pb 1.5 -0.09 0.02 Within accepted values
Cu 100 10.14 1.04 Within accepted values
Zn 150 3.31 0.11 Within accepted values

Discussion
Zinc, copper, and lead in C. iredalei that were gathered 
from the municipalities of  Dumangas and Barotac 
Nuevo, Iloilo met the The International Shellfish Safety 
and Sanitation Standard’s permissible limits. These heavy 
metals’ comparatively low levels in C. iredalei can be 
ascribed to the sampling locations’ seclusion from mining 
operations and industrial industries. The farms where the 
C. iredalei were gathered and isolated from other rivers in 
the area. According to Noman et al. (2022), contemporary 
mining and farming methods have the potential to 
contaminate aquatic biological systems, which in turn may 
affect the levels of  heavy metals in aquatic invertebrates 
like C. iredalei.
Zinc and copper were the most prevalent metals found 
because of  Cu and Zn-based agricultural products that 
are widely used in nearby shrimp and fish-rearing ponds. 
The levels of  these heavy metals were found to be 
consistent with the findings of  Pakingking et al. (2022) 
in their examination of  slipper oyster farming areas of  
the Cogon and Palina Rivers and Cabugao Bay (in Roxas 
City and the Municipality of  Ivisan, respectively, Capiz 
Province, Western Visayas, Philippines). Concentrations 
of  lead, cadmium, mercury, and chromium, meanwhile, 
were below the legal thresholds established by the 
US and the EU. The Food and Drug Administration. 
Additionally, research by Ochoa et al. (2013) found that 
the concentrations of  heavy metals in oysters cultivated in 
Catalonia, Spain’s Ebro Delta were largely similar to those 
found in earlier studies conducted in various unpolluted 
areas. This suggests that the higher exchange rate with 
marine water in bays where oysters are grown results in a 
decrease in metal levels.
Since zinc and copper are regarded as necessary nutrients 
for the typical growth and development of  C. iredalei, the 
comparatively greater quantities of  these elements are 
to be expected (Ochoa et al., 2013). According to Pan 
and Wang (2009), aquatic invertebrates contain copper, 
and the bioaccumulation of  this element might rise 
in direct proportion to the size of  the animal. Natural 
cofactors in enzymatic processes within cells are Zn and 
Cu, which occur as ions (Zn2+ and Cu2+), and high levels 
of  these metals are obtained by C. iredalei through their 
diet. Because Pb has been frequently linked to human 
poisonings, periodic monitoring of  harmful metals in 
oysters should continue even though the concentration 
was below permissible levels (Balali-Mood et al., 2021).
According to this study, C. iredalei can be safely 
consumed because heavy metals like lead, copper, and 
zinc were within permissible bounds. However, ongoing 
observation is necessary.

Only the quantity and interpretation of  lead, copper, and 
zinc from C.iredalei samples collected between March 31 
and April 7, 2024, from the municipalities of  Dumangas 
and Barotac Viejo, Iloilo, are covered by the findings.

CONCLUSION
As of  the last week of  March and the first week of  April 
2024, the levels of  lead, copper, and zinc in C. iredalei from 
Dumangas and Barotac Nuevo were within the permissible 
range established by the International Shellfish Safety and 
Sanitation Standard. In terms of  heavy metal intoxication 
during those months, the C. iredalei samples were safe 
to eat. It is advised that heavy metals, such as Cu, Pb, 
and Zn, be continuously monitored in C. iredalei, not just 
in Dumangas and Barotac Nuevo, Iloilo, but across the 
region. Measuring the concentrations of  chromium, iron, 
and cadmium might also help future studies build on the 
current findings.

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