Organohalogen Residues of Fishes from Different Trophic Levels

Abstract

Global contexts on human health hazards through pesticide residues become a serious focus and environmental issues today. Fishes are used extensively for environmental monitoring because they uptake contaminants directly from water and food. Generally the ability of the fish to metabolize organohalogen is moderate, thus contaminants load in fish are well reflective of the state of pollution in surrounding environments. The present study was conducted to assess the concentrations and patterns of organohalogen pesticide residues i.e. DDT and its metabolites (4,4́-DDT, 2,4́- DDT, DDD and DDE) in fishes and prawn species of different trophic levels of four seasons from Sonargaon Upazila of the Meghna River. The samples were collected between the periods of 2015-2016. The number of species available in the seasons varied from twenty-two to twenty-four i.e. rainy season (twenty-four), autumn (twenty-two), winter (twenty-three) and summer (twenty-two). Analysis of the samples for DDTs residues were carried out using Gas Chromatograph with Electron Capture Detector (GC-ECD). The samples were extracted by Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) method and the sample extracts were cleaned-up by using H2SO4. Linearities (r2) were > 0.9950 for calibrations. The recoveries were 88.67% - 104.89% (20 ng g-1), 70.10% - 101.32% (10 ng g-1) and 71.64% - 113.83% (5 ng g-1). The limit of detection was found 0.0625 ng g-1 in fish samples. The concentrations of total DDTs residue in fish and prawn tissues of rainy-season, autumn, winter and summer varied between 2.64 ± 0.35 ng g-1 to 191.14 ± 31.18 ng g-1, 16.42 ± 1.90 ng g-1 to 271.50 ± 6.17 ng g-1, 3.88 ± 0.60 ng g-1 to 141.57 ± 10.24 ng g-1 , 157.58 ± 1.15 ng g-1 to 1660.89 ± 157.9 ng g-1 wet weight (ww) respectively. The year round highest concentrations were observed in Bacha ( Eutropiichthys vacha). However the lowest levels of total DDTs were observed in Kachki (Corica soborna) in rainy-season and summer, Khalisha (Trychogaster fasciata) in autumn and Goldachingri (Macrobrachium rosenbergii) in winter. Considering the average concentrations of total DDTs residue of four seasons, the twenty fish and prawn species that analysed in all seasons showed the chronology of Kachki (Corica soborna) < Chanda (Parambassis ranga) < Shing (Heteropnuestes fossilis) < Ghainna (Labeo gonius) < Rui (Labeo rohita) < Systomus sarana (Sharpunti) < Bata (Cirrhinus reba) < Jatpunti (Puntius sophore) < Goldachingri (Macrobrachium rosenbergii) < Foli (Notopterus notopterus) < Boal (Wallago attu) < Gulsha (Mystus cavasius) < Bele (Glossogobius giuris) < Tengra (Mystus vittatus) < Bajari-tengra (Mystus tengra) < Chewa (Pseudapocrypter elongates) < Meni (Nandus nandus) < Borobaim (Mastacembelus armatus) < Poa (Otolithoides pama) < Bacha (Eutropiichthys vacha). The other fishes that analysed in one or two seasons showed the chronology, Kaikka (Xenentodon cancila) < Khalisha (Trychogaster fasciata) <Gutum (Lepidocephalus guntea) < Magur (Clarius batrachus) < Tarabaim (Macrognatus aculiatus) < Shole (Channa striata) < Gojar (Channa marulius). In each season, the variation of DDT contents varied with fish species, when the concentrations in a fish varied between seasons. This might be attributed to the combine influence of the trophic position, feeding habits, lipid contents, physiological activities (metabolism rate, excretion rate and maturation stage etc.) of fishes and meteorological parameters i.e. temperature, humidity and rainfall to the accumulation of DDTs in fish tissues. Overall, the rank orders of average DDTs of different fish and prawn species of different seasons were carnivore > omnivore > herbivore and summer > autumn > rainy-season > winter. From the present study, it could be said that lower residues may be found in herbivores, lean and plant based omnivores and lean and zooplankton based carnivores; medium or higher residues may be found in fatty and animal based omnivores, lean and lower carnivores while much higher residues may be found in the fishes with bottom feeder carnivores, predators and fatty top carnivores. Analysis of total DDTs residues by one way ANOVA with LSD and Tukey HSD tests showed that significant differences in total DDTs between herbivore, omnivore and carnivore (p < 0.05). Highly significant differences between seasons (p < 0.001) were also observed. Pearson correlations analysis showed the positive relationships between DDE and DDD with lipid contents (p < 0.05). Besides, highly significant positive relationships between total DDTs with temperature with (p < 0.001) and negative relationship between humidity with total DDTs (p < 0.01) were observed. DDD (55.54%) was the major contributor to fish and prawn samples in rainy-season and followed by 4,4́ -DDT (16.10%), DDE (14.35%) and 2,4́-DDT(14.00%). In autumn season, the major contributor was DDE (53.11%) and followed by the DDD (31.79%), 2,4́ -DDT(8.52%) and 4,4́-DDT(6.58%). In winter the major contributor was DDE (68.80%) and followed by DDD (18.23%), 2,4́-DDT (7.63%) and 4,4́-DDT (5.33%). In summer, the major contributor was 4,4́-DDT(40.23%) and followed by 2,4́-DDT(27.59%), DDE (18.60%) and DDD (13.58%). Compositional distribution of DDTs and the ratios of (DDE+DDD)/DDTs contributing to the values indicating both recent and past use of DDT in the region. The concentrations of total DDTs in all the samples were within the permissible Maximum Residue Level (MRL) i.e. for human consumption recommended by FAO-WHO. But 20.83% species of rainy-season, 68.18% of autumn, 13.04% in winter and 100% in summer exceeded the maximum admissible limit recommended by European Union. However, 4.55% species of autumn and 36.36% of summer were above concentrations associated with reproductive toxicity in several species of fish. To assess human health risks, Health risk Indexes (HI) of fish and prawn samples were calculated. HIs < 1 in all fish and prawn samples indicating that the fishes are safe to consume but the daily consumption of the fishes together with other contamination in food may cause human health hazard. As DDT is a long persistent and bioaccumulative substance in the environment, intake of significant amount of these poisonous elements with our diet is a matter of great health concern.