Study of Heavy Metals in Abnormal Growth and Development using an Alternate Animal Model: Heterometrus fulvipes

Background: Heavy metals exposure in animals can lead to profound effects on growth and development. There have been incidences of various teratogenic effects in the past due to heavy metals exposure from various sources. The present study was conducted to access the effect of chronic heavy metals exposure in animal models. Methods: An experimental prospective study was performed with viviparous animal Heterometrus fulvipes to access the cumulative effect of chronic heavy metals exposure. H. fulvipes was exposed to mercury and lead; and the effects monitored and documented in different times. Results: Chronic heavy metal exposure had considerable effects in the mother and fetus of H. fulvipes. The effects in mother were represented by the loss of body weight and decrease in hepato-pancreatic weight and hepato-somatic index. Chronic exposure in fetus resulted in decrement in the embryonic length with subsequent reduction in the length and weight of embryos. These studies and results of heavy metals in animal have proven the harmful effects of chronic heavy metal exposure with multitude of questions. The question of particular concern would be how well animal teratology studies will predict the human hazard. Conclusion: It is necessary that the heavy metal toxicity be well documented in humans, and adequate precaution should be taken in the mother and fetus to decrease its detrimental effects in the long run. The primary area of focus could be on the prevention of the birth defects induced by maternal exposure to heavy metals during pregnancy, as well as early prevention of teratogenic effects. Key-wordsHeterometrus fulvipes, Heavy Metals, Hepato-somatic indices, Morphometry -------------------------------------------------IJLSSR----------------------------------------------INTRODUCTION Heavy metals are known to affect the reproduction and development of organisms. Heavy metals have different sources: Mercury (Hg), Chromium (Cr), Nickle (Ni) and Zinc (Zn) are mostly naturally occurring, whereas lead (Pb), Cadmium (Cd), Copper (Cu) and Arsenic (As) are the direct consequence of human environmental pollution . Access this article online Quick Response Code Website: www.ijlssr. com DOI: 10.21276/ijlssr.2017. 3.1. 9 The human health risk of heavy metals exposure is a public health problem. The exposure of heavy metals, in particular Pb, Cd, As, and Methyl mercury (MeHg) directly interfere with brain development and results in cognitive impairment. The exact mechanism of their toxicity is still unknown but their synergistic effect is well defined . Much information has been accumulated on the toxicity of the mercury and lead to humans. There are many reported incidences of heavy metals poisoning due to potential contamination, for instance arsenic and lead, leading to lower cognitive scores in children . Lead and mercury toxicity are linked with the use of nutritional contamination, ayurvedic supplements and skin creams . Seafood is one potential source of mercury, and it has been recommended for limiting its use during the pregnancy . Heavy metals toxicity is implicated in Research Article (Open access) Int. J. Life Sci. Scienti. Res., VOL 3, ISSUE 1 Copyright © 2015-2017| IJLSSR by Society for Scientific Research under a CC BY-NC 4.0 International License Page 801 magnification of estrogen dependent disease in female, including cancer of breast, endometrium, and pregnancy related complications like abortions, still births and pre-term deliveries . Mercury is a very toxic metal and there is no acceptable level of mercury for animal exposure. Mercury can induce damage in development of human at any period. It is a potential neurotoxic, nephrotoxic and immunotoxic. The prenatal exposure of methyl mercury, placenta being a very ineffective barrier, can result in negative fetal impact to central nervous system maturation . Pregnant wistar rats showed that mercury is capable of crossing the placenta, accumulating in fetal organs notably highest concentration in kidney, succeeded liver and brain . Similar to mercury, lead exposures in rats have a profound effect in their memory and overall cognition . Exposure of rats to high levels of lead has been associated with an increased frequency of abortion and premature birth in experimental animals. It is evident that most of the studies on the effects of heavy metals on the maternal animal with extended influence on the embryonic development are confined to mammals and fishes. Little information is available on other viviparous forms, particularly the invertebrates, where viviparity and long gestation period are known to exist. Identifying a good viviparous model for evaluating the effect of heavy metals, drugs and other xenobiotics on fetuses, when mother is exposed or treated is of paramount importance. The scorpion Heterometrus fulvipes with its long gestation period is an ideal organism amongst invertebrates for a study of how the heavy metals affect the embryonic development when maternal animals are treated. An attempt is, there for, made to study the effect of heavy metals on the maternal animal and the embryonic development of the viviparous invertebrate H. fulvipes. The embryonic development depends upon the maternal conditions as the mother provides the nourishment and environment to the embryo. Hence, it is likely that the effect of heavy metal on the mother influence the embryonic development. To further validate the extent of the influence, a study of the effects of mercury and lead on embryonic development as reflected by the changes in the morphological, morphometric and gravimetric parameters of the embryos is undertaken. Parturition is the pride of motherhood. A set of physiological changes occur inside the body of mother during pregnancy and parturition is the outcome of successful embryonic development. The effect of heavy metal on embryonic development, if any, would also reflect in the parturition. Therefore, a study to access and document the effects of the heavy metals on parturition after the administration of cumulative long term doses were performed and documented. MATERIALS AND METHODS An experimental prospective study was conducted in the department of Zoology, Nagarjuna University, Guntur during April 2011 to May 2013 with H. fulvipes by using mercuric chloride and lead acetate to represent mercury and lead respectively for studying the effect of these heavy metals on the maternal and embryonic development. The toxicity of mercury and lead was determined by injecting different concentrations of the heavy metals dissolved in distilled water into batches of test animals through the arthrodial membrane in pedipalp between the hand and the brachium. Control specimens were given corresponding doses of distilled water. Mortality was recorded after 24 hours, for each of the concentration administered. LD50 value was calculated using Finney’s probit method (Finney, 1964), and 1/3 LD50 (mercury-0.042 mg/g body weight and lead-0.58 mg/g body weight) to be administered in the present study . Gravid females collected during latter half of the July were stocked in the laboratory in individual jars and maintained feeding regularly with cockroaches. 1/3 LD50 value of mercury and leadwere administered to the maternal animal for monthly administration of sub-lethal doses of mercury in successive doses during the gestation period. The stock was divided into three groups. Group I received the sub lethal dose of mercury, group II the sub lethal dose of lead and Group III, as a control, received the corresponding dose of solvent (Distilled Water). After a month (mid-September), a batch of gravid females was drawn from each group for studying the effects of first doses of the heavy metals on the maternal animal, on the embryonic development and on the parturition. Rest of the animals in the three groups were administered a second dose of the corresponding heavy metals by midSeptember. After taking samples from the three groups for experimental purposes to evaluate the impact of second dose by mid-October, the remaining ones were administered a third dose. Similarly, the fourth, fifth, sixth, seventh, eighth and ninth doses were administered by the middle of November, December, January, February, March and April respectively after drawing samples every month for experimental purpose. Gravid females drawn each month from the three groups were individually weighed and the weight of the hepatopancreas of each animal was noted using a monopan electrical balance (OWALABOR). Hepato-somatic indices (HIS) were calculated using the following formula: Weight of the Hepato-pancrease HIS = ________________________ X 100 Weight of the animal Samples of gravid females drawn each month from the groups I, II and III were sacrificed to examine cumulative effects of successive monthly doses of mercury and lead on the time course of development and on the morphological, morphometric and gravimetric aspects of developing embryos, using the corresponding group III samples (distilled water treated animals) as controls. Now to study Int. J. Life Sci. Scienti. Res., VOL 3, ISSUE 1 Copyright © 2015-2017| IJLSSR by Society for Scientific Research under a CC BY-NC 4.0 International License Page 802 the morphological features of the embryos, the maternal animals were dissected in scorpion Ringer’s solution and the diverticula containing embryos were fixed in Bouins fixative and preserved in 70% alcohol. Photographs of the diverticula chosen at random were taken before isolating the embryo to provide information on the size and shape of the diverticula which are also known to change in accordance with the development of the embryos. The embryos in the diverticula were isolated and photographs were taken for studying the morphological features of the embryo for studying the morphometry, the length of the embryo during the early month of gestation was measured with the help of an ocular micrometer, in t