Persistent Organic Pollutants In Water, Sediments And Fish From Lake Victoria And Implications To Human Health Risks

EXTENDED ABSTRACT

Lake Victoria is an important freshwater resource in Tanzania and its neighbouringcountries namely Uganda, Kenya, Rwanda, Burundi and the Democratic Republic of Congo(DRC). Millions of people dotted around the lake depend on it as a major source of household and industrial water supply, irrigation, transport and provide for fishing as the main source of animal-derived protein as well as income. In Tanzania, the lake provides employment opportunities to more than four million people engaged directly or indirectly with fishing activities. The frequently fished and consumed fish species that are of commercial interest include; Nile perch (Lates niloticus), Nile tilapia (Oreochromisniloticus) and the freshwater sardines (Rastrioneobola argentea) commonly known as dagga in Tanzania. The fish are further processed to feed the domestic, regional and international markets. Current estimates from the lake put the annual contribution of the fisheries sector to the Tanzanian Gross Domestic Product (GDP) up to 2.5%.

There have been unsubstantiated claims that despite using agrochemicals such as

pesticides in agriculture, some fisher folks have been using such chemicals for fishing and

preservation of fish products during storage. The same organochlorine pesticides are still

in use in agricultural activities within the lake basin and there is a possibility that they

accumulate in water, sediments and fish. Furthermore, there have been incinerations of

medical wastes, discharge of electronic wastes and untreated wastewaters from industrial

establishments in water bodies that tend to increase the loading of polychlorinated

biphenyls (PCBs) in water, sediments and fish. It is likely that human beings will get

exposed to these chemicals through drinking water and eating fish from the lake. 

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The present study overall objective was therefore to assess fish consumersꞌ eating habits

and the prevalence, levels and human health risks of indicator PCBs and OCPs in water,

sediments, fish and fish products from Lake Victoria in Tanzania.

The specific objectives of the study were:

i. To establish levels of indicator PCBs and OCPs in water, sediments and fish from

Lake Victoria.

ii. To determine the prevalence and quantify residual levels of indicator PCBs and

OCPs in processed fish products from Lake Victoria.

iii. To assess fish consumersꞌ eating habits.

iv. To evaluate the probable human health risks associated with consumption of

persistent organic pollutants (POPs) contaminated fish and fish products from

Lake Victoria.

Water and sediment samples were collected from twelve nationally designated sampling

points (considered as important hotspots). Thirty six samples of both water and sediments

(a total of 72 samples) were collected for analysis. A total of 162 fresh fish samples were

collected from nine selected landing sites and 480 samples of processed fish products

from Kirumba Fish Market for analysis of POPs. Extraction of the samples was done

using a QuEChERS method and POPs analysis using a gas chromatography equipped

with electron capture detectors (GC-ECDs) and a gas chromatography equipped with

mass spectrometry (GC-MS).

A questionnaire was also administered to 122 fish consumers to assess the fish

consumption habits and patterns. The main focus of administering the questionnaire was

to identify the types of fish species consumed, frequencies of fish consumption, quantities 

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of fish consumed and factors affecting fish consumption in the population around the

lake.

The results showed that some organochlorine compounds were present in water,

sediments, fish and fish products from Lake Victoria in Tanzania. This is likely due to

human anthropogenic activities being undertaken along the lake, long range atmospheric

transport and environmental persistence of the compounds. For water samples, the

∑PCBs ranged between 0.95 and 2.24 µg/L while for sediments the range was between

because of their structures and high degree of chlorination. For OCPs; Aldrin and

Dieldrin were the highest (6.13 ±0.90 and 6.82±0.53 µg/kg- dw, respectively) and p,

pꞌ- DDT was the lowest (0.82±0.12 µg/kg- dw) in sediments whereas for water samples

the highest concentration was γ- HCH (1.60±0.32 µg/L) and the lowest was α- endosulfan

(0.15±0.01 µg/L).

There were high levels of organochlorine compounds in sediments than the water samples

suggesting that sediment serves as a sink for organochlorine pollutants and therefore act

as a source of these compounds in case of environmental changes. However, the levels of

POPs measured in water and sediments in this study were far below the Maximum

Residual Limit (MRL) set by FAO/WHO and the European Union (EU) except Aldrin

and Dieldrin through which based on the Threshold Effect Concentration (TEC) for

freshwater ecosystems, Aldrin and Dieldrin are the only OCPs that seem to be a threat to

Lake Victoria environment. 

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For the fresh fish species which were considered in the current study; L. niloticus and O.

niloticus, the results revealed that fish species sampled were undersize, reflecting

overfishing and abuse of bylaws.

The abuse may be going beyond overfishing and touching other environmental protection

bylaws. The results showed further that four organochlorine pesticides (β-HCH, HCB,

Aldrin and Dieldrin) were identified in fresh muscles of L. niloticus and O. niloticus at

measurable quantities at concentration between