PhD

The present investigation was undertaken for the first time to assess the level of contamination of mercury (Hg) and Cadmium (Cd) in the soil, water, plants and biosamples in localities where there is significant duck population and to study the pathological effects of these chemicals and ochratoxin A (OA) with special reference to immune response in the ducks and duck embroys. The residues of these chemicals in various tissues of the ducks were also assessed.
Hg and Cd were detected in all the samples from all the localities surveyed and its presence especially in the soil, vegetation, fish, liver and kidney of the ducks from these areas indicated its public health significance.
After the administration of OA, HgCl2 and CdCl2, there was dose dependent embryo mortality and reduction in hatchability rate. The mortality percentage in the highest dose group of embryos inoculated with HgCl2, Cdcl2 and OA was 55%, 51.6% and 48.3% respectively while the hatchbility rate was 29.92%, 35% and 47.83% respectively. This clearly indicated the embryotoxic action of these chemicals. The body weight, weight of the thymus, and the bursa of Fabricius was found lowered in the embryos inoculated with these chemicals. The variations noticed in the weights at different periods of observation between the chemicals were also dose dependant. The weight of the spleen of the embryos inoculated with OA and HgCl2 was comparable to the normal embryo but with CdCl2, it was found significantly lowered in the highest dose group at the 28th day of incubation. These observations, therefore indicated that Cd has an adverse significant biological effect on the lymphoid organs of the developing embryo. Similar effect was observed with Hg and OA but was relatively low. Histologically, depletion of the lymphoid elements consequent to degeneration, necrosis and cytolysis was the characteristic feature in the bursa of Fabricius and thymus, however, it was comparatively less in the spleen.
Ultrastructural changes in the lymphoid cells in all these organs showed membrane alterations, mild to severe mitochondrial changes, ribosomal detachment and fragmentation of RER and nucleolar and nuclear changes indicative of cell damage, and marked reduction in differentiation into plasma cells. Epithelial cells were also found affected. The toxic effects of these chemicals were more or less similar in the bursa of fabricius, intensity and severity being more with CdCl2 followed by HgCl2 and OA in that order. In the thymus, also, CdCl2 caused severe pathological effects while with HgCl2 intensity was least. In the spleen there was increased erythrophagocytosis in addition to these changes and was more severe with HgCl2.
In the liver, severe necrobiotic changes were found in the hepatic cells associated with ultrastructural picture of organellar damage and lytic changes in the nucleus.
Intensity of these changes was more severe in CdCl2 treated embryos followed by those treated with OA and with HgCl2. In the kidney, the cellular alterations were more in the proximal convoluted tubules and the intensity of these alterations was less in OA and CdCl2 treated embryos compared to those treated with HgCl2. The embryos inoculated with OA, HgCl2 and CdCl2, revealed degenerative changes in the lymphoid and other organs. The adverse immunobiological effects of OA, Hg and Cd on the developing embryo were established by histological and ultrastructural studies.
In the ducks, OA, HgCl2 and CdCl2 were fed orally (at the rate of 300 ug, 10mg and 15 mg/kg body weight respectively) for 90 days. Clinically ducks showed dullness, restlessness and unusual hyperresponsiveness and inco – ordination of movement, in OA, HgCl2 and CdCl2 fed ducks respectively at the later stage of the experiment. Progressive reduction in the gain of the body weight, of the bursa of Fabricius was noticed in all the groups (OA, HgCl2 and CdCl2 treated) while that of the thymus was noticed mainly in CdCl2 and OA treated ducks.
There was highly significant reduction in the total erythrocyte count (TEC), Haemoglobin (Hb) concentration and Packed Cell Volume (PCV) in the groups fed OA, HgCl2 and CdCl2. Highly significant leucopaenia with relative heterophilia and lymphocytopenia was observed in OA and HgCl2 fed ducks, while highly significant leucocytosis with heterophilia and lymphocytopenia was seen with CdCl2 fed ducks. These alterations revealed the toxic action of these chemicals on the haemopoietic cells and the formed elements of the blood.
Estimation of the haemagglutination inhibition (HI) antibody titre, total serum protein (TSP), serum globulin (SG) and serum IgG and IgM levels clarified the adverse effect of OA, Hg and Cd on the humoral immune system, which was evident at an early stage in Cd and Hg treated ducks while at a later stage in OA fed ducks. There was marked reduction in the serum IgM and IgG level in response to New Castle disease Virus (NDV) in ducks fed HgCl2 and CdCl2 respectively.
The highly significant reduction in the T – lymphocyte count in the peripheral blood, increase in the migration indices in response to NDV in leucocyte migration inhibition test (LMIT), reduction in cutaneous response to phytohaemagglutinin – M (PHA – M), 2, 4 – dinitrochlorobenzene (DNCB) and the decreased spleen indices in Graft versus host reaction (GVHR) indicated the toxicity of OA and Cd on the cell – mediated immunity, which was more pronounced and evident at an early stage in Cd treated ducks than compared to OA treated ducks. However, the results of the migration indices, PHA – M cutaneous response and GVHR demonstrated that the CMI response escape the toxic insult of the Hg and is dependant on the duration of exposure, which was clarified by T – cell dependant lymphocytopaenia and reduction in cutaneous response to DNCB at the last week of the experiment. Significant reduction in the phagocytic ability in all the ducks treated either with OA, HgCl2 or CdCl2 was observed by carbon clearance assay.
There was reduction in the weight of the bursa of Fabricius and spleen. The thymus showed focal areas of congestion and petechiae in Cd induced toxicity, and was found appreciably reduced and atrophied with Cd and at later stages with OA. Degenerative and retrograde changes indicative of necrobiosis were observed histologically. Ultrastructural changes were more severe with CdCl2 followed by HgCl2 and OA in that order. In the spleen of ducks fed CdCl2 there were proliferative changes initially followed by degenerative changes at later stages. In the thymus, effect of the Cd was more severe on the lymphocytes followed by OA and was least with HgCl2.
Histological and ultrastructural studies revealed degenerative nephropathic changes in the kidney associated with Hg, OA and Cd toxicity. Intensity of alterations was more with Cd.
The hepatic lesions characterised by moderate to severe hepatosis were more pronounced in the case of Hg and Cd in an increasing order. Histological and electron microscopic studies elucidated the neuropathological changes associated with Hg, Cd and OA toxicity.
Estimation of OA, Hg and Cd residues indicated a steady increase in the accumulation of these substances in the various tissues depending on the dose and duration of exposure. Highest concentration of OA, Hg and Cd was detected in the kidney, followed by liver. Residues of these substances at varying concentrations were also detected in the muscles, brain, spleen, bursa of Fabricius and thymus.
This study brought to light the immunosuppressive effect of OA, Hg and Cd which would compromise the dichotomous defence mechanism of the ducks. Also adverse effects on hepatic, haemopoietic, reneal and nervous system were documented. It was clarified by this investigation that immunotoxic effect of these chemicals could lead to breakdown of immunity and outbreak of diseases when the ducks are maintained in a polluted environment. The need for the systematic monitoring of the environment and taking appropriate steps to prevent environmental pollution were stressed. The public health importance of residues of these chemicals was brought to light.