Threats of hazardous chemicals in the food chain: The Philippine Mallard duck model

In the past, raising ducks along the shores of Laguna Lake became a common practice due to the availability of native duck feeds such as snails, small fish, shrimps and calms. However, there were events that created massive changes in areas or localities along the Laguna de Bay coastal lines where ducks are raised. At present, the Laguna Lake is a huge sink for solid and liquid waste coming from coastal residents, agricultural enterprises, livestock farms, industries, and also from fishery activities. Majority of the households discharge their solid and liquid wastes into the lake. Thus, it is always assumed that the ducks feed such as snails, bivalves, shrimps and fishes which come from the lake are contaminated by these wastes which could have been one of the causes of declining duck egg production. Some hazardous substances may have dissolved or suspended in the water column or accumulated in sediments and result in an array of adverse ecological effects. Pollution from industries, domestic wastes, and transportation within the lake threatens the various forms of agricultural enterprises such as the duck industry that depend on snails and small fish populations. The deteriorated condition of the lake could be the major reason for the death of duck farming industry in several coastal towns of Rizal and Laguna [Philippines]. The laboratory interventions used in the experiments to assess the influence of selected hazardous chemicals, at low levels of contamination, yielded alarming results. Exposure of mallard drakes to Beta-BHC (100 ppb in feed) resulted to poor semen color and consistency, and decreased spermatozoa in the ejaculate. In addition, treatment of female mallard ducks with 0.34 and 0.67 ppm cadmium, alone or in combination with 66.67 ppb Beta-BHC in feed resulted to higher hepatosomatic index (HSI), liver abnormalities, increased oviductosomatic index (OCI), and abnormalities in ovary and ovidust. Ael liver samples of Mallard ducks exposed to cadmium and Beta-BHC showed hematoma. Another type of lesion was white nodules which was observed in liver of ducks treated with cadmium alone and of those treated with estradiol. Necrosis was evident in the liver samples of Mallard ducks treated with cadmium alone and of those treated with estradiol. Necrosis was evident in the liver samples of Mallard ducks treated with cadmium, Beta-BHC or estradiol. Other observed histopathologic lesions include hemorrhage and vacuolar degeneration. Ovaries of ducks exposed to different hazardous chemicals were characterized by macroscopic lesions and underdevelopment. Degenerated, deformed,and underdeveloped follicles were also found. Microscopically, most of the ovaries had the same histopathological lesions. Atretic follides, mononuclear cells infiltration, congestion, and fibrosis were evident. The presence of cadmium and other contaminants in the water and sediments in Laguna Lake, and in conventional and commercial feeds of ducks sends an alarm to all duck raisers, with greater concern in the positive detection of contaminants in fresh eggs and liver samples from untreated ducks. These present a very serious implication for the health not only of the animals but also of the consuming public who occupies the highest position in the food chain.