@Copyright 1987 by The Humana Press Inc. All rights of any nature, whatsoever, reserved. 0163-4984/87/1200-0389502.2{)
Factors Affecting Tissue Distribution of Heavy Metals Age Effects and the Metal Concentration Patterns in Common Terns, Sterna hirundo MICHAEL GOCHFELD *'1 AND JOANNA BURGER 2
'Department of Environmental and Community Medicine, and Joint Graduate Program in Toxicology U/~DNJ Robert Wood Johnson Medical School, Piscataway, NJ 08854; and 2Department of Biological Sciences and Bureau of Biological Research, and Joint Graduate Program in Toxicology, Rutgers University, Piscataway, NJ 08854
ABSTRACT Metal distribution in an organism at any one time is a resultant of many extrinsic and intrinsic factors. Improved analytic methodology has made it feasible to obtain highly sensitive determinations for many metals in a single sample. Thus, it is now feasible to examine patterns of metal distribution. We report on a study of the effect of age on metal patterns in the common tern, Sterna hirundo, a fisheating seabird. We contrast the levels of nine metals in the liver of adult and young terns and compared these with levels in tern eggs. Unlike many previous studies, adults did not have significantly higher levels of metals, although for most metals, levels in eggs were significantly lower than liver levels of young and adults. The intermetal correlations showed more significant positive correlations for adults and eggs than for chicks, the latter showing instead a correlational chaos, probably reflecting the immaturity of their physiologic defense mechanisms and the absence of dynamic equilibrium. Index Entries" Metals, factors affecting tissue distribution of; metal concentration; mercury; cadmium; cobalt; chromium; copper; lead; manganese; nickel; zinc; aluminum; metal excretion; metallothionein; Sterna hirundo; common tern. *Author to whom all correspondence and reprint requests should be addressed. Biological Trace Element Research
389
Vol. 12, 1987
Gochfeld and Burger
390
INTRODUCTION Numerous studies of metal concentrations in birds traditionally provide insights on the metal distributions at a single point in time, usually the time of death. From this we have constructed our understanding of the dynamics or natural history of metals moving among the many fluid and tissue compartments of the body, as a result of the processes of absorption, transport, modification, storage, and excretion. Each of these processes is subject to numerous effects, yet only recently has it become possible to provide sufficient analyses to understand these processes. Many studies using animals as biological indicators of environmental contamination have demonstrated concentration differences in different habitats. Studies showing differences among species are often interpreted as reflecting either differences in the foods chosen or the habitats occupied. Even studies of a single species often attribute individual differences to food or habitat variation. Such studies often miss the other factors that might account for differences among groups of individuals (e.g., sex or age). Further, they may miss the significance of metal dynamics revealed by the pattern of intermetal correlations. Factors affecting metal distribution can be divided into: (1) Factors relating to the metal (species, concentration). (2) Factors inherent to the host (species, sex, age, genetics, essentiality of the metal). (3) Acquired host factors (health, nutrition, state of enzyme induction). (4) Concurrent events (including other metal exposures). (5) Environmental factors (geography, habitat, substrate). In this paper we examine metal concentrations as a function of age in the common tern, Sterna hirundo, a nearly cosmopolitan (i.e., worldwide) small seabird that nests commonly on the shores of Long Island and New Jersey. We will test our hypotheses by comparing the median values for different age groups and by examining the correlation matrices among the metals.
Age Differences Age differences in heavy metal levels have been reported (Table 1). If the tissue levels of metals were compared for adult and young individuals of a population, differences could arise because of the way that the individuals process and store particular metals, or they could reflect the past exposure to the metals and the fact that the adults will presumably have had much longer exposure to the circumstance and the metals. Field studies, such as Eskildsen and Grandjean (1) on lead in swans' blood or Hoffman and Curnow (2) on mercury in herons, find significantly higher tissue concentrations in adult than young. The likely interpretation is that adults have had a longer duration of exposure. This is confirmed in experimental studies, such as Cain et al. (3), who showed a Biological Trace Element Research
Vol. 12, 1987
391
Factors Affecting ?4etal Distribution
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Factors Affecting Tissue Distribution of Heavy Metals Age Effects and the Metal Concentration Patterns in Common Terns, Sterna hirundo MICHAEL GOCHFELD *'1 AND JOANNA BURGER 2
'Department of Environmental and Community Medicine, and Joint Graduate Program in Toxicology U/~DNJ Robert Wood Johnson Medical School, Piscataway, NJ 08854; and 2Department of Biological Sciences and Bureau of Biological Research, and Joint Graduate Program in Toxicology, Rutgers University, Piscataway, NJ 08854
ABSTRACT Metal distribution in an organism at any one time is a resultant of many extrinsic and intrinsic factors. Improved analytic methodology has made it feasible to obtain highly sensitive determinations for many metals in a single sample. Thus, it is now feasible to examine patterns of metal distribution. We report on a study of the effect of age on metal patterns in the common tern, Sterna hirundo, a fisheating seabird. We contrast the levels of nine metals in the liver of adult and young terns and compared these with levels in tern eggs. Unlike many previous studies, adults did not have significantly higher levels of metals, although for most metals, levels in eggs were significantly lower than liver levels of young and adults. The intermetal correlations showed more significant positive correlations for adults and eggs than for chicks, the latter showing instead a correlational chaos, probably reflecting the immaturity of their physiologic defense mechanisms and the absence of dynamic equilibrium. Index Entries" Metals, factors affecting tissue distribution of; metal concentration; mercury; cadmium; cobalt; chromium; copper; lead; manganese; nickel; zinc; aluminum; metal excretion; metallothionein; Sterna hirundo; common tern. *Author to whom all correspondence and reprint requests should be addressed. Biological Trace Element Research
389
Vol. 12, 1987
Gochfeld and Burger
390
INTRODUCTION Numerous studies of metal concentrations in birds traditionally provide insights on the metal distributions at a single point in time, usually the time of death. From this we have constructed our understanding of the dynamics or natural history of metals moving among the many fluid and tissue compartments of the body, as a result of the processes of absorption, transport, modification, storage, and excretion. Each of these processes is subject to numerous effects, yet only recently has it become possible to provide sufficient analyses to understand these processes. Many studies using animals as biological indicators of environmental contamination have demonstrated concentration differences in different habitats. Studies showing differences among species are often interpreted as reflecting either differences in the foods chosen or the habitats occupied. Even studies of a single species often attribute individual differences to food or habitat variation. Such studies often miss the other factors that might account for differences among groups of individuals (e.g., sex or age). Further, they may miss the significance of metal dynamics revealed by the pattern of intermetal correlations. Factors affecting metal distribution can be divided into: (1) Factors relating to the metal (species, concentration). (2) Factors inherent to the host (species, sex, age, genetics, essentiality of the metal). (3) Acquired host factors (health, nutrition, state of enzyme induction). (4) Concurrent events (including other metal exposures). (5) Environmental factors (geography, habitat, substrate). In this paper we examine metal concentrations as a function of age in the common tern, Sterna hirundo, a nearly cosmopolitan (i.e., worldwide) small seabird that nests commonly on the shores of Long Island and New Jersey. We will test our hypotheses by comparing the median values for different age groups and by examining the correlation matrices among the metals.
Age Differences Age differences in heavy metal levels have been reported (Table 1). If the tissue levels of metals were compared for adult and young individuals of a population, differences could arise because of the way that the individuals process and store particular metals, or they could reflect the past exposure to the metals and the fact that the adults will presumably have had much longer exposure to the circumstance and the metals. Field studies, such as Eskildsen and Grandjean (1) on lead in swans' blood or Hoffman and Curnow (2) on mercury in herons, find significantly higher tissue concentrations in adult than young. The likely interpretation is that adults have had a longer duration of exposure. This is confirmed in experimental studies, such as Cain et al. (3), who showed a Biological Trace Element Research
Vol. 12, 1987
391
Factors Affecting ?4etal Distribution
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