Ecotoxicology 2, 33-40 ( 1993)

Mercury dynamics in young Common Tern (Sterna hirundo ) chicks from a polluted environment P E T E R H. B E C K E R .1, R O B E R T W. F U R N E S S 2 and D I A N A H E N N I N G 1 l lnstitut fiir Vogelforschung, An der Vogelwarte 21, D-2940 Wilhelmshaven-15, Germany 2Applied Ornithology Unit, Zoology Department, Glasgow University, Glasgow G12 8QQ, UK

Received 25 March 1992; accepted 28 June 1992

We studied mercury concentrations and amounts in tissues of 19 starved young Common Tern chicks (median age 4 days) and in eggs from the same colony. Concentrations and burden were similar between eggs and newly hatched chicks. Mercury concentrations were highest in down, which contained at least 38% of the body mercury. The mercury burden of the whole body and of the tissues as well as the concentration in down increased with age and body mass, indicating the importance of down as an elimination pathway. Conversion ratios between mercury concentrations in tissues and the whole chick body varied according to the contamination level.

Keywords: mercury; body distribution; feather concentrations; body burden; tern chicks Introduction

Bird hatchlings are especially at risk from toxic chemicals that accumulate in the egg to high concentrations, as these may influence embryonic development, or the critical period of hatching and the first days of the hatched chick. As levels of chemicals in food are almost always lower than in eggs, body concentrations of chemicals decrease with advancing growth and age of the young, because of dilution and excretion (e.g., Becker and Sperveslage, 1989; Scharenberg, 1991). In this context, the heavy metal mercury is of special interest: mercury accumulates in birds' eggs and has embryotoxicological effects (e.g., reviews in Ohlendorf et al., 1978; Fimreite, 1979; Scheuhammer, 1987); on the other hand, birds are able to decontaminate their body by putting mercury into the growing down and feathers (B~ickstr6m, 1969; Furness et al., 1986; Braune and Gaskin, 1987a,b; Lewis and Furness, 1991), binding methyl mercury into feather keratin (Thompson and Furness, 1989). In Black-headed Gull Larus ridibundus chicks dosed with mercury, Lewis and Furness (1991) found 65% of the body burden of mercury in the completed plumage. In this paper we report the distribution and dynamics of mercury in Common Tern Sterna hirundo hatchlings from the German Wadden Sea, an area highly polluted with mercury. Among the species breeding there, Terns have highest egg-mercury levels (Becker et al., 1985; Becker, 1991). We examined mercury concentrations as well as *To whom correspondence should be addressed. 0963-9292 © 1993 Chapman & Hall

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Becker, Furness and Henning

burdens in tissues and in the entire body, depending on the age and body mass of the young Terns. Methods

Study site, collection of birds and eggs The samples originate from a Common Tern colony of 105 pairs, breeding in the harbour of Wilhelmshaven (53.27 N 08.07 E) at the Jade, southern German North Sea coast. This colony has been very productive in other years (Becket, 1991). In 1991, however, almost all chicks from clutches of the first laying cycle died through predation or starvation (see Results). Under license of the Bezirksregierung Oldenburg, during June and July 1991 we collected 19 freshly dead chicks from nine broods (single chicks from two broods, two siblings from four broods, three siblings from three broods). Before their death the chicks had been weighed every second day by a digital balance to the nearest g. The chicks as well as 13 eggs from nine other clutches (failing to hatch or deserted) of the same colony were frozen at - 1 8 °C after collection and prior to further treatment.

Sample preparation and mercury analysis After thawing the chicks, as much as possible of the down was plucked, weighed and stored. The liver was dissected out. Egg contents and down- and liver-flee chick's bodies were homogenized. After weighing (_+1 mg) all wet samples were dried to constant weight in an oven at 50 °C. The samples were digested in a 1:4 mixture of concentrated nitric and sulfuric acids. Total mercury concentrations were determined by a cold vapour technique using a Data Acquisition Ltd DA 1500-DP6 Mercury Vapour Detector (Furness et al., 1986) with detection levels of about 0.01 pg per g fresh weight. The ratio between fresh and dry weights being known for each sample, mercury concentrations are presented on dry and on flesh weight bases. In addition, the total amount of mercury ("burden") in the tissues, the rest of the body or in the entire body or egg is given in pg. The concentration in the whole chick body was calculated from body burden and chick mass.

Statistical analysis As both inter- and intraclutch variation contribute significantly to the variance of mercury levels in Common Tern eggs (Becker, 1992), the levels in chicks and eggs, respectively, were analysed as independent samples, irrespective of being related by the same clutch. The data were not significantly different from a normal distribution (Kolmogorov-Smirnov one-sample test, Norusis, 1986). The values are given as arithmetic mean _+ I standard deviation. The significance of differences between tissues of chicks was tested by the nonparametric Friedman test, by the Wilcoxon-Wilcox multiple rank test for related samples, and that between chicks and eggs was by the Mann-Whitney Utest. To test correlations, the Spearman rank correlation coefficient was used. All tests were two-tailed, and the level of significance was ~< 0.05.

Mercury in Common Tern chicks

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Results

Mercury concentrations and distribution in the body of chicks Concentrations and burden of mercury were significantly different between down, liver, and the rest of the chick's body (Friedman test p ~

Mercury dynamics in young Common Tern (Sterna hirundo) chicks from a polluted environment.

: We studied mercury concentrations and amounts in tissues of 19 starved young Common Tern chicks (median age 4 days) and in eggs from the same colony...
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