Dietary Hg Research Articles

Mercury exposure in breeding common loons (Gavia immer) in central Ontario, Canada

AbstractTotal Hg concentrations were determined in blood and feather samples of breeding common loons (Gavia immer) and their chicks from 24 lakes in Ontario with a range of water chemistry and fish Hg concentrations. In paired comparisons, males had significantly higher blood (p < 0.005) and feather (p < 0.05) Hg concentrations than their female mates. Sex differences in Hg concentrations were attributable to size differences between the two sexes and to the possible transfer of Hg to eggs by females during egg‐laying. Significantly higher blood (p < 0.001) and feather (p < 0.01) Hg concentrations were found in adult loons compared to their chicks. Adult blood Hg concentrations were significantly correlated with those of their chicks (r = 0.62, p < 0.05). Adult blood concentrations averaged about 13 times those of corresponding chicks. Both adult and chick blood Hg concentrations were positively correlated with fish Hg concentrations (r = 0.71 and 0.51, respectively), indicating that adult loons in central Ontario, like their chicks, probably feed mainly on their breeding lakes and reflect the fish Hg concentrations of those lakes. Three of 24 lakes had 20‐ to 50‐g fish (mainly perch and sunfish) with Hg concentrations at or exceeding the critical concentration (0.3–0.4 μg/g wet weight or ∼1–2 μg/g dry weight) reported to cause reproductive impairment in loons. Monitoring Hg in blood (adult and chick) and feathers (chicks only) is useful for assessing the local bioavailability of methylmercury and the degree of current dietary Hg exposure in loons and other piscivorous birds.

EFFECTS OF MERCURY ON WILDLIFE: A COMPREHENSIVE REVIEW

Wildlife may be exposed to mercury (Hg) and methylmercury (MeHg) from a variety of environmental sources, including mine tailings, industrial effluent, agricultural drainwater, impoundments, and atmospheric deposition from electric power generation. Terrestrial and aquatic wildlife may be at risk from exposure to waterborne Hg and MeHg. The transformation of inorganic Hg by anaerobic sediment microorganisms in the water column produces MeHg, which bioaccumulates at successive trophic levels in the food chain. If high trophic level feeders, such as piscivorous birds and mammals, ingest sufficient MeHg in prey and drinking water, Hg toxicoses, including damage to nervous, excretory and reproductive systems, result. Currently accepted no observed adverse effect levels (NOAELs) for waterborne Hg in wildlife have been developed from the piscivorous model in which most dietary Hg is in the methyl form. Such model are not applicable to omnivores, insectivores, and other potentially affected groups, and have not incorpotated data from other important matrices, such as eggs and muscle. The purpose of this paper is to present a comprehensive review of the Hg literature as it relates to effects on wildlife, including previously understudied groups. We present a critique of the current state of knowledge about effects of Hg on wildlife as an aid to identifying missing information and to planning research needed for conducting a complete assessment of Hg risks to wildlife. This review summarizes the toxicity of Hg to birds and mammals, the mechanisms of Hg toxicity, the measurement of Hg in biota, and interpretation of residue data.

Tissue-level biomarkers and biological effect of mercury on sentinel slugs, Arion ater.

The present investigation was to determine the extent to which mercury (Hg) provokes measurable effects on the structure of the digestive gland of slugs as well as to relate the extent of these effects to the cell and tissue distribution of Hg. For this purpose, slugs (Arion ater) received various dietary concentrations of Hg (from 0 to 1,000 microg Hg/g food) as chloride for 30 days and were histologically examined every third day. Autometallography was used to demonstrate Hg as black silver deposits (BSD) in paraffin sections. The lysosomes and residual bodies of digestive cells resulted to be the major accumulation sites. In addition, Hg was also evidenced in lipofuscine granules of vacuoles in excretory cells but, however, it was rarely observed within calcium cells. Generally, the extent of BSD increased with dietary Hg concentration and exposure time but, however, it became significant lowered after exposure to 1,000 microg Hg/g food for 30 when the digestive epithelium appeared almost devoid of digestive cells. On the other hand, significant changes were recorded in the quantitative structure of digestive tubules. Mean Epithelial Thickness (MET), Mean Luminal Radius (MLR) and Mean Diverticular Radius (MDR) were recorded as measures of the sublethal biological effect of Hg. MET, MLR/MET and MET/MDR were affected by Hg concentration (C), exposure time (T) and CxT interaction, changes in MET, MLR, MLR/MET and MET/MDR being explained by regression models after logarithmic transformation of the data. In order to explain the nature of the changes in the quantitative structure of the digestive tubules this investigation was complemented with qualitative histological observations. According to them, the excretory activity in digestive cells was initially enhanced. Afterwards, the relative numbers of digestive cells declined until the extreme cases of exposure to 1, 000 microg Hg/g for 27 to 30 days in which the digestive epithelium was mostly comprised of calcium and excretory cells. Concomitantly, some changes took place in blood vessels where Leydig cells became disrupted and the connective tissue layers thickened. Finally, it is suggested to use slugs in soil quality assessment as sentinel organisms ("Slug Watch") in which biomarkers of exposure to metallic pollutants and of biological effect are recorded.

Selenium-Mercury Interaction during Intestinal Absorption of 75Se Compounds in Chicks

The effects of inorganic (HgCl2) and organic (CH3HgCl) mercury on the intestinal absorption of Se compounds [Na275SeO3, Na275SeO4, L-[75Se]methionine ([75Se]Met)] were determined in 3-wk-old White Leghorn cockerels by the in vivo ligated duodenal loop procedure. The intraduodenal dose contained 0.05 µCi 75Se, 0.01 mM Se, 150 mM NaCl and 0–1.0 mM Hg. In the presence of 1 mM inorganic Hg in the intraduodenal dose, the absorption of the inorganic 75Se compounds was only about 65% of that in the control group, whereas only a slight inhibitory effect on [75Se]Met absorption was observed. Methylmercury had no effect on [75Se]selenite absorption. Precipitation of the 75Se-selenite in the intestinal lumen partly explained the direct interaction between inorganic Hg and Se compounds. Absorption of [75Se]Met and [75Se]selenite was also determined in chicks fed after hatching a purified diet supplemented with varying amounts of Hg (0–500 mg/kg) and Se (0–4 mg/kg). Dietary Hg significantly reduced the transfer of [75Se]selenite to body by enhancing the accumulation of the isotope in the intestinal tissue. Dietary Hg did not affect the absorption of [75Se]Met, but altered the whole-body distribution of this Se compound. Because interaction between Se and Hg was observed mainly between the inorganic compounds and with use of a manyfold excess of Hg over Se, the data suggest that intestinal interaction between these metals is not of great nutritional importance.

Effects of dietary lead, cadmium, mercury, and selenium on fatty acid composition of blood serum and erythrocyte membranes from chicks

A series of experiments was conducted to study the effects of dietary and injected lead (as Pb acetate-3H2O) and of dietary Cd, Hg, and Se on fatty acid composition of serum lipids of chicks as measured by gas-liquid chromatography. The effect of dietary Pb on fatty acid composition of erythrocyte membranes was measured also. Dietary Pb (1000 ppm) increased the serum concentration of arachidonic acid (20:4, first no. = no. of carbon atoms:second no. = no. of double bonds) and decreased the concentration of linoleic acid (18:2) and the ratio 18:2/20:4. Intraperitoneal injection of Pb (52 mg/100 g body weight) did not alter serum fatty acid composition by 4 h post-injection. The separate effects of 2000 ppm Pb, 60 ppm Cd, 500 ppm Hg, and 10 ppm Se added to the diet on serum fatty acids were measured in a single experiment. In comparison to controls, Pb and Cd lowered serum concentration of 18:2. Only Pb raised serum 20:4. Pb lowered the ratio 18:2/20:4, whereas Cd and Hg raised the ratio and Se was without effect. Dietary Pb (2000 ppm) raised the concentration of 20:4 and lowered the ratio 18:2/20:4 in erythrocyte membranes. The different effects of injected and dietary Pb on the serum 18:2/20:4 ratio suggest that Pb alters 20:4 synthesis from 18:2 rather than mobilization of 20:4 from tissues. The Pb-induced increase of lipid peroxida-tion in erythrocytes observed by other workers may be a reflection of increased 20:4 level in erythrocyte membranes.

Interaction of mercury and water deprivation on growth, feed consumption, and mortality in chickens.

The objectives of the present study were (1) to assess the effects of dietary Hg treatment, dehydration, and Hg treatment combined with dehydration on growth, feed and water consumption, and mortality in young chickens, and (2) to determine if the effects persisted following a 14-day recovery.

Distribution of mercury and selenium in egg components and egg-white proteins.

Methylmercuric chloride (Hg) at 20 ppM and sodium selenite (Se) at 8 ppM were fed, separately and in combination, to laying hens. Oral doses of CH/sub 3//sup 203/HgCl and H/sub 2//sup 75/SeO/sub 3/ also were given to all hens. The concentration of /sup 203/Hg and /sup 75/Se in egg white and egg yolk, and the distribution of the radioisotopes among proteins of egg white, were determined. The highest concentrations of /sup 203/Hg were observed in egg white. The 8 ppM of dietary Se significantly increased the concentrations of /sup 203/Hg in egg white when compared with a diet containing no added Se. At the same time, the addition of Se to the diet reduced /sup 203/Hg in the egg yolk. /sup 75/Se was found primarily in egg yolk, but 20 ppM dietary Hg significantly decreased /sup 75/Se in the egg yolk and increased it in the egg whites. A significant Hg x Se interaction was observed for deposition of /sup 75/Se in egg white. When dietary Hg was fed separately from dietary Se, /sup 75/Se deposition was increased in the egg whites. More than 97% of the total /sup 203/Hg in egg white was associated with ovalbumin. Similarly, total Hgmore » was found in greatest quantities in ovalbumin, irrespective of the addition of dietary Hg or Se. The largest proportion of total /sup 75/Se dose and the highest concentration of total Se per unit of protein occurred in globulin, especially when 8 ppM Se were fed. The data illustrate preferential binding of Hg by ovalbumin and of Se by globulin as compared with other major proteins of egg white.« less

Influence for Distribution in Broiler Carcass of Minerals in the Feed

Distribution of arsenic (As), fluorine (F), cadmium (Cd), lead (Pb), mercury (Hg) and copper (Cu) in the muscle, skin, liver, heart, kidney and feather of meat-type cnicks was determined after feeding experimental diets containing various levels of salts of these elements to one-day-old chicks for 8 weeks.Sensitivity limit of determination of As, F, Cd, Pd, Hg and Cu was 0.1, 1.0, 0.01, 0.1, 0.01 and 0.1ppm, respectively. Content of As, F, Cd, Pb and Cu in the basal diet mainly composed of yellow corn, soybean meal, fish meal and alfalfa meal was 0.1, 120, 0.06, 0.4 and 8.7ppm, respectively. Mercury was not detected in the diet.With the supplementation of As at the level of 7.9ppm or less, small amount of less than 0.36ppm was determined in the edible parts.Content of Cd and Cu in the edible parts of the chicks was proportional to the level in the diet. The highest value of Cd, i. e., 2.36ppm, was observed in the kidney and that of Cu, i. e., 5.62ppm, was observed in the liver of the chicks fed the diets with supplementation of the highest level of these elements, respectively.Only small amount of mercury, less than 0.02ppm, was found in the muscle, heart, gizzard and skin of the chicks fed the diet containg 0.49ppm or less of supplemented Hg.Content of Hg in the liver was slightly higer, being less than 0.06ppm. Content of Hg in the kidney seemed to be proportional to dietary Hg level, and to reach plateau at the dietary level higher than 0.13ppm.Content of the elements except Cd and Hg in the feather was much higher than that in the edible parts of the chiks. The highest level of As. F. Pb and Cu was 3.14, 24.6, 0.2 and 8.34ppm, respectively, in the feather of the chicks fed the diets containing high level of the elements. The highest level of Cd and Hg in the feather was 0.13 and 0.04ppm, respectively.