Occurrence and potential health risks of indicator polychlorinated biphenyls in selected marine fish species: a case study of Dar es salaam
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Date
2023-03
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Sokoine University of Agriculture
Abstract
Polychlorinated biphenyls (PCBs) are industrial chemicals in a group of persistent organic
pollutants (POPs) that are ubiquitous in environments including water bodies. Ocean
sediments are one of the major reservoirs of PCBs, contaminated through runoff water,
atmospheric transfer, and sewer discharge of industrial and municipal wastes, risking
contaminating aquatic organisms. Fish are vulnerable to contamination because PCBs are
highly lipophilic and can easily be absorbed and stored in fish fatty tissues. However, there
are limited studies on the marine fish contamination status in Tanzania's coastal waters.
The overall objective of the present study overall objective was to assess the occurrence
and levels of indicator PCBs in selected species of marine fish in Dar es Salaam, and the
specific objectives were to determine indicator PCBs levels in mackerel fish (Rastrelliger
kanagurta) and rabbitfish (Siganus sutor) and to assess the dietary exposure and health
risks of PCBs to artisanal fishermen and fish vendors.
Fish samples were randomly collected from fishermen and fish vendors at Kivukoni Ferry fish
market where a total of 60 fresh fish samples were collected from two different species,
Rastrelliger kanagurta, and Siganus sutor, chosen based on the prior conducted food
consumption survey. A food frequency survey was conducted among fishermen and fish
vendors to assess the fish consumption habit of the respondents. PCBs extraction and
sample matrix clean-up were done using the QuEChERS method and quantification analysis
of PCBs was done using a Gas Chromatography tandem Mass Spectrometer (GC-MS/MS) at
the Government Chemist Laboratory Authority (GCLA) laboratories.
Results showed the presence of indicator PCBs in both fish species, with 73.3% of
R. kanagurta samples and 20% of S.sutor samples showing PCBs contamination. The levels
of the six indicator PCBs were relatively low in both fish species with the highest mean
concentration (∑6PCBs), 3.71 ngg-1 w/w observed in R. kanagurta. The individual mean
levels of detected indicator PCBs ranged from <LOD to 1.15 ngg-1 w/w, while the sum of the
six indicator PCBs (∑6PCBs) levels ranged from 0.12 to 3.71 ngg-1 w/w. PCBs contamination
was dominated by the three congeners PCB 138, 153, and 180, while PCBs 28, 52, and 101
levels were below the limit of quantitation (<LOD).
The finding of this study indicates PCBs contamination of fish in the study area due to the
historical release of PCBs. R. kanagurta were found to have significantly higher PCBs
contamination levels than the S. sutor fish species due to differences in trophic levels and
feeding habits. However, detected PCBs levels in both fish species were below the
maximum residue limits (MRL) of 75 ngg-1 w/w set by the European Commission (UC).
The potential human health risks as a result of PCBs contaminated fish consumption were
assessed for the general population for both children and adults. Estimated lifetime cancer
risks were very low ranging from 5.14E-09 to 6.14E-07 for both children and adults, below
the recommended health guidelines of <10E-6 for adults and <10E-04 for children.
Estimated non-carcinogenic risks hazard indices were far less than the critical value of 0.1,
ranging from 1.95E-06 to 3.26E-05 for both children and adults, indicating that consumption
of the R.kanagurta and S. sutor fish species from the Kivukoni Ferry fish market would have
negligible adverse health effects to the general population.
The results of the fish consumption survey showed that R. kanagurta and S. sutor were the
most preferred fish for consumption among fishermen and fish vendors due to their
availability in the daily catch and lower prices and therefore more affordable to be used as a
meal. Moreover, fishermen and fish vendors were found to consume an average amount of
400.5 g day-1 of fish which were higher than the national per capita fish consumption of 8.22
kg (23 g day-1) and global per capita consumption of 20.5 kg (56 g day-1).
Dietary exposure and potential health risk of PCBs to artisanal fishermen and fish vendors
were estimated using the fish consumption rate obtained in the initial food frequency survey
and compared to that of the general population estimated using national per capita fish
consumption. The average intake of total PCBs by fishermen and fish vendors was higher in
comparison to that of the general population ranging between 5.10 and 27.56 ngkg-1 bw.day-
1 for normal and higher fish consumers depending on the estimation scenario, while that of
the general population ranged between 0.14 and 0.31 mg kg-1 bw.day-1
in lower and upper
estimation scenario respectively. The average daily intake of total PCBs by fishermen and
fish vendors exceeded the recommended tolerable daily intake, (TDI) of 20 mg kg-1 bw.day-1
in high fish consumers while the estimated lifetime carcinogenic and non-carcinogenic
hazard indices exceeded the recommended health guidelines of <10E-6 and 0.1
respectively, raising serious concerns for potential adverse health effects in long run.
However, the estimated average daily intake of total PCBs for the general population was far
below the recommended guidelines for an average intake of total PCBs and the
carcinogenic and non-carcinogenic hazard indices estimation was also far below the
recommended health guideline of <10E-6 and 0.1 respectively.
PCBs exposure through the intake of fish was observed to be a course of serious concern
for fishermen and fish vendors, due to exposure to high levels of PCBs that exceeded
recommended health guidelines for tolerable daily intake.
To safeguard the most vulnerable fish consumers from PCBs exposure, the development of
cost-effective strategies to minimize the accumulation of PCBs in aquatic ecosystems and
environments is required. Creation of awareness among fish consumers on the potential
adverse health risks of PCBs and the different ways to minimize exposure such as species
diversification to reducing consumption of fish species that are more vulnerable to PCBs
contamination such as fatty fish, carnivorous and omnivorous fish while consuming more of
herbivorous and low-fat fish species.
Description
MSc.-Dissertation in Food Quality and Safety Assurance
Keywords
Polychlorinated biphenyls, Marine fish, Mackerel fish, Rabbitfish