26 



poisoning, but no particular studies have been 

 made on the toxicity of heavy metals to sea- 

 birds (Parslow et al. 1973). However, in 

 certain terrestrial species, symptoms of poi- 

 soning might be expected when mercury con- 

 centrations in liver or kidney tissues reach 

 about 30ppm (W. H. Stickel 1971). By con- 

 trast, normal levels are less than 1 ppm. 



Although death may not have been caused 

 by mercury poisoning, mercury in the livers of 

 adult great egrets found dead in California 

 ranged between 2 and 9.5 ppm (Faber et al. 

 1972). Mercury in the liver (22 ppm; 98 ppm 

 dry weight) of a gannet from the Irish Sea 

 could have caused the bird's death (Parslow et 

 al. 1973). 



Female mallards fed 3 ppm mercury (dry 

 weight) as methyl mercury in their diet had 

 average mercury residues of 11.1 ppm in their 

 livers, 14.7 ppm in their kidneys, 5.0 ppm in 

 their muscles, 4.6 ppm in their brains, and 

 5.5 to 7.4 ppm in their eggs (Heinz, 1976a). 

 Males had higher residues, and many of the 

 ducklings from these parents died within 

 1 week after hatching (Heinz 1974, 1976a). 

 The ducklings also had high levels of mercury 

 in their tissues. 



In short-term tests of lethal dietary toxicity 

 of pesticidal chemicals, Ceresan M, a fungi- 

 cide containing ethyl mercury, was relatively 

 more toxic to young mallards than were 37 

 other compounds (Heath et al. 1972a). Only 

 endrin and Dasanit were more toxic. In simi- 

 lar subsequent tests, Morsodren, another 

 organomercurial fungicide, was also highly 

 toxic to young mallards (Hill et al. 1975). 



Mercury potentiated the toxicity and 

 biochemical effects of parathion in coturnix 

 quail fed a sublethal concentration of Morso- 

 dren (4 ppm dry weight as methyl mercury) 

 for 18 weeks (Dieter and Ludke 1975). Mean 

 residue concentrations in these birds were 

 21 ppm of mercury in the liver and 8.4 ppm in 

 the carcass. The computed LD 50 of parathion 

 was 5.86 mg/kg in birds not fed Morsodren 

 and 4.24 in those fed the heavy metal. When 

 challenged with a sublethal oral dose of para- 

 thion (1.0 mg/kg), Morsodren-fed birds ex- 

 hibited significantly greater inhibition of 

 plasma and brain cholinesterase activity than 

 controls. 



After administration of various mercury 

 compounds to domestic chickens (Gallus 

 gallus), the methyl mercury compounds were 



rather evenly distributed among the organs, 

 whereas the other mercury compounds, or- 

 ganic and inorganic, gave very high concen- 

 trations in the liver and kidneys compared 

 with other organs (Kiwimae et al. 1969). Dif- 

 ferences in the proportion of methyl mercury 

 compounds to total mercury occurred in the 

 white and the yolk of the eggs from these 

 hens. Although the proportion in the white 

 was similar to that in the blood and the 

 muscles, the proportion in the yolk was simi- 

 lar to that in the liver and the kidneys. The al- 

 bumen contained mainly methyl mercury 

 compounds in concentrations that varied with 

 the compound given to the hens. The methyl 

 mercury concentration in albumen was 

 always much lower when other compounds 

 were administered than when the hens were 

 given the same quantity of methyl mercury 

 hydroxide. 



In another study, mercury was not detect- 

 able in the albumen but was present at high 

 levels in the yolk following intravenous injec- 

 tion of mercuric nitrate into laying coturnix 

 quail (Nishimura et al. 1971). 



Evaluation of enzymatic profiles appears to 

 be a potentially valuable technique for moni- 

 toring the presence of toxicants in wild popu- 

 lations, especially if used to complement 

 standard chemical residue analysis (Dieter 

 1975). Lactate dehydrogenase activity in- 

 creased twofold and cholinesterase activity 

 decreased in birds fed Morsodren. After feed- 

 ing for 3 weeks, mercury in starling carcasses 

 reflected the concentrations fed daily, 

 whereas the concentration in the livers was 

 2 to 4 times that in the diet. 



A decrease in cholinesterase activity oc- 

 curred in male coturnix quail that were fed 

 diets for 12 weeks containing graded levels of 

 mercuric chloride (Dieter 1974). At 12 weeks 

 the decrease was proportional to the log dose 

 received, although this was not true after 

 2 and 4 weeks on the treated diet. Mercury 

 residues attained in the tissues were 5% or 

 less of those in the feed. 



There was a marked sexual difference in 

 rates of mercury loss in coturnix quails (Back- 

 strom 1969). Males lost little of the mercury 

 in their bodies, especially from the brain and 

 muscle, in 30 days, but females had a marked 

 loss in this period, largely because of excre- 

 tion in eggs. Ring-necked pheasants lost 33% 

 to 50% of the mercury from their livers and 



