Occurrence of pesticide Residues in fish Meat
Overall, Gas chromatography laboratory analysis of the 37 fish muscle samples 37.84% was positive for OCPs. This analysis study indicated that six pesticide residues including Endosalfan I; Endosalfan II, Endosalfan sulfate, 4, 4, DDE, 4, 4, DDD, and 4, 4, DDT residues were detected (Table 1). This study finding was different from Gustav Gbeddy et al., (2012) who founds in 100% tested samples which is higher than the present study. Another higher frequency of occurrences of OCPs detected by Bedigama and Gabadage, (2018) in Srilanka was 80%.
The detection levels were from not detected for Dimethotes (detection limit = 0.001 µg/ kg), to 4041.73 µg/kg dry weight for Endosalfan I recorded in the present study (Table 1).
Table 1
Organochlorine pesticides (OCPs) detected in Lake Tana Fishes (n = 37)
No
|
OCPs
|
Range (µg/kg)
|
Over all Mean ± SD (µg /kg)
|
1
|
Endosalfan I
|
0.001–4041.73
|
341.50 ± 32.19
|
2
|
Endosalfan II
|
ND − 628.27
|
36.01 ± 2.3
|
3
|
Endosalfan sulfate
|
ND-146.69
|
5.43 ± 4.06
|
4
|
4, 4, DDE
|
ND -227.11
|
64.01 ± 9.08
|
5
|
4, 4, DDD
|
ND-55.59
|
5.65 ± 3.12
|
6
|
4, 4, DDT
|
ND to 42.76
|
1.58 ± 0.3
|
Endosalfan and its metabolites concentrations in fish muscle were recorded up to mean of 341.50 ± 32.19 µg/kg. A study conducted in Uganda by Bagumire et al., (2008) showed lower level (< 2µg/kg) of endosalfans in fish muscle; Polder et al., (2014) documented in fish muscle of lakes of Tanzania, that endosulfan level was from ND – to 405µg/kg. Study done by Deribe, et al., (2014) in fish muscle of lake Hawassa, Ethiopia noted Endosalfan, ND – 42.5µg/kg which is lower than the present result. In Gana, a study conducted by Kuranchie-Mensah et al., (2013) endosulfan reported a concentration of 0.01–7.52 µg/kg. Another study in Bénin by Yehouenou et al., (2014) noted endosulfan of 9–215 µg/kg concentration.
In our finding the mean concentration of 4, 4, DDT and its metabolites was recorded 1.58 to 64.01µg/kg (Table 1). Similar with our finding the study done by Deribe et al., (2014) in fish muscle of lake Hawassa, Ethiopia detects mean concentration range of 19–56 µg/kg of 4, 4, DDT. Another comparable study was done by Yohannes et al., (2014) in edible fish species from a Rift Valley lake-Lake Ziway in Ethiopia, the concentration of 4, 4; DDT was 0.77–61.9 µg/kg. Different studies done by different scholars globally including Gustav Gbeddy et al., (2012) in Ghana was found the mean DDTs residue concentration in fish muscles ranges from 10 -1700.35 µg/kg; another study done by Adu-Kumi et al (2010) in lakes of Ghana reported up to 440.90 µg / kg and Polder et al., (2014) in Tanzania was recorded 7.2–319 µg/kg indicates the concentration levels of 4, 4, DDT was higher than our finding. A study done in Srilanka with an average of 735 µg/kg; 4, 4, DDT was detected which were higher than the present finding (Bedigama and Gabadage, 2018). Lower than our findings were detected in study done by Kasozi et al (2006), that DDTs in fish samples from Lake Victoria, Uganda was 0.80–0.86µg/kg. Another lower concentration of dry weight DDTs in fish muscle was reported in studies conducted in Africa; in Egypt by Yahia and Elsharkawy, (2014) noted 0.70–0.90 µg/kg; in Bénin by Yehouenou et al., (2014) stated 3.88–11.3 µg/kg and in Kenya study by Omwenga et al., (2016) quantified 2.098 µg/kg.
This high occurrence in our study area might be due to the long-term use of organochlorine pesticides to improve agricultural productivity in the catchments of the Lake. The high lipophilicity, bioaccumulation nature, long half-life and potential of long range leaching nature of the chemicals results in accumulation of persistence toxic substances in soil, water and air (USEPA, 2009, Agrawal et al., 2010, Ravindran et al., 2016). The tropical conducive pests’ multiplication environment of the water shed of Lake Tana might lead to the use of OCPs frequently and indiscriminately by the farmers (Kannan et al., 1995, Birhan and Marshet, 2020). In addition, lack of proper implementation of legislation, improper market regulations, poor knowledge and skill of safety use of OCPs and ignorance shown by the farmers, agricultural workers in the Lake Tana catchment may prone to experience high levels of agricultural chemicals, including OCPs (Mengistie et al., 2016, Beyene et al., 2016, Birhan and Marshet, 2020).
In our finding the detected level of 4, 4, DDT was relatively lower than its metabolites (4, 4, DDE and 4, 4, DDD) and also similarly the Endosalfan sulfate concentration in fish muscle was lower than its metabolites (Endosalfan I and Endosalfan II) (Table 1). This the lower concentration of the parent compounds might indicate that currently limited use of those persistence OCPs around Lake Tana catchments. The detected concentration may be due to previous historic event with long half-life (2-15Years) (Augustijn-Beckers et al., 1994). However non negligible concentration of parent compound of this persistence pollutants were detected that indicates still in use of these OCPs in the water shed of Lake Tana.
This study highlights that more pesticide was detected from African catfish (Clarias gariepinus) species than other main commercially important fish groups (Labeobarbus spp. and O. niloticus) Fig. 1.
Similar to our finding study conducted by Nicklisch et al., (2017) high variation in pesticide levels have been observed when examining different fish species. Spatial wise, occurrence was frequent at Gorgora, Enferanze and Bahir Dar sampling sites of the study Lake. This variability distribution of OCPs in our study area might be due to the environment as well as the biological factors like amounts of lipid in their body and difference in ecological characteristics of the fish species (Borga et al., 2004). Different studies indicated that factors that influence OCPs pollutant levels in fish muscle such as fish length, fish species, its trophic level, habitat type, feeding habitat, and fish movement patterns and residence time in contaminated areas (Borga et al., 2004, USEPA, 2009, Cardona, 2015, Bonito et al., 2016).
Public Health Risk
Humans represent one of the top receptors for aquatic contaminants and consumption of fish with high levels of contaminants may pose public health concerns. The consumption of contaminated fish may lead to serious public health treat if the concentration level is higher than maximum residue level (MRL) and acceptable daily intake (ADI) standards of FAO/WHO, (2009); U.S. FDA, (2009) and EU, (2013). The amount of OCPs residue concentration found in some fish meat samples of our study was higher than the recommended MRL of different standards. However, except Endosalfan I the overall mean value of concentration detected in our study was lower than MRL standards of FAO/WHO, (2009), U.S, FDA, (2009), EU, (2013)(Fig. 2).
These higher concentrations of endosalfan I in fish muscle originated from Lake Tan North West Ethiopia, indicating that it is alarming to the people who consume fish food.
Another method that health risk assessment of consumers from the intake of OCPs contaminated fish was done by calculating health risk index (HRI). In our finding the mean concentration detected was higher than the acceptable daily intake of WHO/FAO recommended. The acceptable daily intake of Endosalfan I; Endosalfan II, 4, 4, DDE, 4, 4, DDD recommended by WHO/FAO, (2009) is 20, 20, 5, 5 µg/kg respectively. Due to low per capital consumption rate of fish in Ethiopia, the present finding of a HRI ranges from 0.002 to 0.1275 indicating the present level has no public health risk (Table 2).
Table 2
ADIs, EDIs of OCPs residues and their HRI associated with the consumption of fish from the Lake Tana
Pesticides
|
Range (µg/kg)
|
Mean ± SD
|
ADI
|
EDI
|
HRI
|
Health Risk
|
Endosalfan I
|
0.001–4041.73
|
341.50 ± 32.19
|
20
|
2.55
|
0.1275
|
No
|
Endosalfan II
|
ND − 628.27
|
36.01 ± 2.3
|
20
|
0.27
|
0.0135
|
No
|
Endosalfan sulfate
|
ND-146.69
|
5.43 ± 4.06
|
20
|
0.04
|
0.1275
|
No
|
4, 4, DDE
|
ND -227.11
|
64.01 ± 9.08
|
5.0
|
0.48
|
0.096
|
No
|
4, 4, DDD
|
ND-55.59
|
5.65 ± 3.12
|
5.0
|
0.04
|
0.008
|
No
|
4, 4, DDT
|
ND to 42.76
|
1.58 ± 0.301
|
5.0
|
0.01
|
0.002
|
No
|
Where ADI: acceptable daily intake, EDI: estimated daily intake; HRI health risk index; SD: Standard deviation; ND: not detected |
But these values may pose potential public health risk if the HRI is calculated considering local per capita consumption. This minimum exposure with no public health risk (HRI<1) was recorded indifferent studies; for instance in Ghana by Gbeddy et al., (2012) and Akoto et al., (2016). Differently to our finding; study done by Yohannes et al. (2014) from a Rift Valley Lake-Lake in Ziway, Ethiopia, indicated a potential cancer risk from consumption of the fish from the calculated hazard ratio. Another study in Srilanka by Bedigama and Gabadage, (2018) found HRI values more than 1.
As Limitation of this study; it is necessary to conduct further studies that assess the detection of OCPs residues in human serum to examine burden of these OCPs and integrating biomarkers of exposure and health risk effects, and modeling exposure routes via fish consumption.