Toxic and essential trace elements in adolescents

There is a need for knowledge of trace element levels in different population groups. Several applications can be identi ed. One is as reference levels that can be used to detect changes in environmental exposure. Another is to reveal de ciency of essential elements, or in some cases toxicity. Toxic elements need to be monitored, as the exposure may be close to levels where adverse effects can arise. Absorption of elements occurs via the gastrointestinal tract and the lungs, and the absorbed fraction may depend on the route of exposure. Diet is the main source of exposure to trace elements in the general population that are not occupationally exposed. Toxic elements may enter the food chain through contamination of the environment, e.g. through atmospheric deposition or naturally high levels in soil. Essential elements are widespread in most foods, as they are also essential to plants and animals used for food production. Adolescents constitute a little studied group in regard to trace element levels in blood. They have a high recommended energy and nutrient intake per kg body weight. Moreover, a high energy intake may expose them to more toxic trace elements via the diet than adults. However, many adolescents do not consume an adequate diet and may therefore risk de ciency of essential elements. In a longitudinal Swedish nutritional survey, almost 400 adolescents (boys and girls) were sampled for blood and serum at the ages of 15 and 17 years for a trace element study within the survey. The adolescents were living in the two Swedish cities, Uppsala and Trollhättan. The cities differ in that Trollhättan has long had metal industries such as several smelters, while Uppsala is a university city, with almost no industrial metal emissions. The two cities also represent different socioeconomic structures, with a higher percentage of the adolescents’ parents having university-level education in Uppsala. The elements analysed were the well-known toxic elements cadmium, mercury and lead, as well as the essential elements cobalt, copper, zinc and selenium (1). The elements rubidium, platinum, palladium, rhodium, thallium and tungsten were also analysed. The analytical method used was inductively coupled plasma mass spectrometry (ICP-MS), which enables rapid and simultaneous multielement analyses. The trace element concentrations were then related to the adolescents’ age, gender, socioeconomic status and residential area (city) (2). It should be noted that the age factor may also re ect temporal changes in environmental exposure. This is mainly relevant for toxic elements. The in uence of  sh consumption on mercury and selenium concentrations, and of dental amalgam  llings on mercury concentrations, was also investigated (3). The adolescents’ blood concentration of lead was low from an international perspective, and also decreased between 15 and 17 years of age (2, 4). Decreasing blood lead has been reported in conjunction with decreasing use of leaded petrol, but the present decrease may also be a result of dilution of body burden in the growing adolescents. There was also a signi cant difference in blood lead concentration between Uppsala and Trollhättan (pB0.0005, F ig. 1). Boys had higher levels of lead in the blood than did girls. Reasons for a gender difference may be a higher haematocrit, or a higher energy intake in the boys. The levels of cadmium in blood were signi cantly higher in smokers than in non-smokers (pB 0.0005). Blood cadmium was also positively in uenced by socioeconomic status (2). The reason for this relationship is not obvious, but the higher consumption of vegetables in the higher socioeconomic groups may play a role, as vegetables are one of the main food groups contributing cadmium to the diet. It was shown that in this study population,  sh consumption was a statistically signi cant predic-

There is a need for knowledge of trace element levels in different population groups.Several applications can be identi ed.One is as reference levels that can be used to detect changes in environmental exposure.Another is to reveal deciency of essential elements, or in some cases toxicity.Toxic elements need to be monitored, as the exposure may be close to levels where adverse effects can arise.Absorption of elements occurs via the gastrointestinal tract and the lungs, and the absorbed fraction may depend on the route of exposure.
D iet is the main source of exposure to trace elements in the general population that are not occupationally exposed.Toxic elements may enter the food chain through contamination of the environment, e.g. through atmospheric deposition or naturally high levels in soil.Essential elements are widespread in most foods, as they are also essential to plants and animals used for food production.
Adolescents constitute a little studied group in regard to trace element levels in blood.They have a high recommended energy and nutrient intake per kg body weight.M oreover, a high energy intake may expose them to more toxic trace elements via the diet than adults.H owever, many adolescents do not consume an adequate diet and may therefore risk de ciency of essential elements.In a longitudinal Swedish nutritional survey, almost 400 adolescents (boys and girls) were sampled for blood and serum at the ages of 15 and 17 years for a trace element study within the survey.The adolescents were living in the two Swedish cities, Uppsala and Trollha ¨ttan.The cities differ in that Trollha ¨ttan has long had metal industries such as several smelters, while U ppsala is a university city, with almost no industrial metal emissions.The two cities also represent different socioeconomic structures, with a higher percentage of the adolescents' parents having university-level education in U ppsala.
The elements analysed were the well-known toxic elements cadmium, mercury and lead, as well as the essential elements cobalt, copper, zinc and selenium (1).The elements rubidium, platinum, palladium, rhodium, thallium and tungsten were also analysed.The analytical method used was inductively coupled plasma mass spectrometry (ICP-M S), which enables rapid and simultaneous multielement analyses.The trace element concentrations were then related to the adolescents' age, gender, socioeconomic status and residential area (city) (2).It should be noted that the age factor may also re ect temporal changes in environmental exposure.This is mainly relevant for toxic elements.The in uence of sh consumption on mercury and selenium concentrations, and of dental amalgam llings on mercury concentrations, was also investigated (3).
The adolescents' blood concentration of lead was low from an international perspective, and also decreased between 15 and 17 years of age (2,4).D ecreasing blood lead has been reported in conjunction with decreasing use of leaded petrol, but the present decrease may also be a result of dilution of body burden in the growing adolescents.There was also a signi cant difference in blood lead concentration between U ppsala and Trollha ¨ttan (p B 0.0005, F ig. 1).Boys had higher levels of lead in the blood than did girls.R easons for a gender difference may be a higher haematocrit, or a higher energy intake in the boys.The levels of cadmium in blood were signi cantly higher in smokers than in non-smokers (p B 0.0005).Blood cadmium was also positively in uenced by socioeconomic status (2).The reason for this relationship is not obvious, but the higher consumption of vegetables in the higher socioeconomic groups may play a role, as vegetables are one of the main food groups contributing cadmium to the diet.
It was shown that in this study population, sh consumption was a statistically signi cant predic-  tor of mercury in both blood and serum (3), even though the adolescents consumed only a few sh meals per month.H owever, the concentrations of selenium in blood and serum were not in uenced by sh consumption.The highest selenium concentrations were found in boys from U ppsala, and the lowest in girls from Trollha ¨ttan (2).The number of dental amalgam llings signi cantly in uenced the mercury concentration in serum (3).

Trace elements in adolescents
Essential trace elements are regulated by homoeostatic mechanisms in the body, and it is important to take this into account when interpreting analytical data.The copper levels increased with age in the girls, probably because of hormonal changes during puberty (p B 0.006, F ig. 2).The concentration of serum copper was also elevated in 17-year old smoking girls compared with non-smokers (p B 0.0005, F ig. 2).The cobalt concentration was higher in girls, while boys had higher levels of zinc in serum.N one of the essential elements was in uenced by socioeconomic status (4).
R esidential area signi cantly in uenced each of the 13 analysed elements (4).The differences in element levels, however, were in different directions, e.g.blood lead levels were higher in Trollha ¨ttan, while serum mercury was higher in U ppsala.Therefore, there was no clear evidence that the higher metal emissions in Trollha ¨ttan caused these differences.
This study demonstrates the impact of several factors on trace element levels in adolescents, thus showing the relevance of reporting the subjects' background in detail in trace element studies.

Fig. 1 .
Fig. 1.Blood lead (mg l ¼ 1 ) in adolescent s from the Swedish cities U ppsala and Trollha ¨ttan at the ages of 15 (15-y) and 17 years (17-y).The box is de ned by the upper and lower quartiles, with the median marked by a subdivision of the box.The whisker s are the lines that exten d from the top and bottom of the boxes to the lowest and highest observations, excluding outliers (circles) with values that are more than 1.5 box-length s from the median.