Correlation between urine and blood concentrations, and dietary intake of cadmium and lead among women in the general population of Japan

Objective: To examine whether lead (Pb) in urine and cadmium (Cd) in blood, especially the former, can be used as markers of environmental exposure of general populations to these metals. Methods: Between 1991 and 1998, spot urine and peripheral blood samples, together with 24 h duplicates of food intake were collected from 607 non-smoking adult women in 30 survey sites (SS) in seven administrative regions all over Japan. Urine, blood and food duplicate samples were analyzed by inductively-coupled plasma spectrometry, for Cd and Pb in urine (Cd-U and Pb-U), in blood (Cd-B and Pb-B) and in food duplicates (Cd-F and Pb-F). Correlation between the measurements was examined by regression analysis. Results: The Cd-B correlated closely with Cd-U, and both Cd-B and Cd-U with Cd-F, on an individual basis (n = 607), on an SS basis (n = 30) and on a regional basis (n = 7). The Pb-U however did not correlate with Pb-B on a regional basis although they correlated with each other when analyzed on an individual as well as SS basis. Moreover, the correlation coefficients between Pb-U and Pb-B were much smaller than those between Cd-U and Cd-B. Neither Pb-U nor Pb-B showed significant correlation with Pb-F on any levels of statistical analysis. Conclusions: Both Cd-B and Cd-U can be employed as biomarkers of environmental Cd exposure. The reliability of Pb-U for use in place of Pb-B appeared to be small. Received: 21 January 1999 / Accepted: 2 November 1999     

电感耦合等离子体质谱法快速测定血液尿液中的铅和镉

目的:建立一种能同时测定血液尿液中铅和镉的方法。方法:用0.1%Triton X-100-0.5g/LED-TA-2%氨水混合溶液稀释血液和尿液,然后直接用电感耦合等离子质谱仪测定铅镉的含量。结果:铅镉的方法检出限分别为0.181μg/L和0.189μg/L,样品测定的精密度<6%,铅的回收率在92.2%～115.6%之间,镉的回收率在103.1%～107.2%之间。对冻干牛血(GBW09139g、GBW09130g)、冻干人尿铅(GBW09105e)、冻干人尿镉(ZK018-2)中铅和镉的含量进行了分析,测定值与标准参考值吻合。结论:本方法快速灵敏,精密度和准确度均符合要求,结果令人满意。     

Background exposure of urban populations to lead and cadmium: comparison between China and Japan

Objectives: To assess and compare the background exposure of the general population to lead (Pb) and cadmium (Cd) in China and in Japan. Methods: Food duplicates and peripheral blood samples were collected from nonoccupationally exposed subjects, viz 202 Chinese women in four Chinese cities (Beijing, Shanghai, Nanning, and Tainan) and 72 Japanese women in three Japanese cities (Tokyo, Kyoto, and Sendai) in the years 1993–1995. Wet-ashing and graphite furnace atomic absorption spectrometric methods were used for the determination of Pb and Cd levels in food and blood samples. Results: Geometric mean (GM) dietary Pb intake (25.8 μg/day) and the GM Pb concentration in blood (56.7 μg/l) in Chinese were significantly higher than in Japanese women (11.6 μg/day in food and 32.1 μg/l in blood), whereas Cd in food (32.1 μg/day) and Cd in blood (1.92 μg/l) in Japanese were significantly higher than in Chinese women (9.9 μg/day in food and 1.07 μg/l in blood). The intake of Pb and Cd via boiled rice accounted for 3.6% and 31.1% of the total dietary burden in Chinese, and 12.1% and 32.7% in Japanese, respectively. The Cd burden was acquired almost exclusively through the dietary route, whereas the Pb burden came from both air and food, especially in the case of the Chinese population. Conclusions:  The background Pb exposure in the Chinese population was higher than that in the Japanese population, whereas Cd exposure was lower in Chinese women than in their Japanese counterparts. Received: 4 March 1996 / Accepted 3 May 1996     

Determination of cadmium and lead in urine of some Nigerian subjects

Forty-one urine samples of smokers and non-smokers from Ile-Ife, Nigeria were analyzed for normal cadmium and lead levels after acid digestion. Results of the preliminary study show that concentrations of cadmium obtained were generally low compared with lead. The mean urinary levels from non-smokers ranged from 0.05 - 0.02 to 0.16 - 0.01 wg ml-1 and from 0.02 - 0.03 to 0.88 - 0.04 wg ml-1 for cadmium and lead respectively, whilst, for smokers, urinary levels varied between 0.07 - 0.01 and 0.23 - 0.02 wg ml-1 and between 0.28 - 0.03 and 1.02 - 0.02 wg ml-1 were obtained for cadmium and lead, respectively. Cd levels in urine of smokers and non-smokers are higher than the recommended normal level of 0.0085 wg ml-1, while levels of Pb are above the 0.08-0.15 wg ml-1 exposure range. Results of spiking experiments with urine gave high percentage recoveries for both elements (Cd, 87.9 - 0.40%) and (Pb, 90.40 - 0.12%). Blank determination was done for background correction.     

Nonoccupational exposure to agricultural work and risk of urinary bladder cancer among Egyptian women

This study examined the associations between nonoccupational exposure to agricultural work, through husband or head of household (H/HH) occupation, and urinary bladder cancer risk among Egyptian women. A total of 1,167 women (388 bladder cases and 779 age- and residence-matched, population-based controls) from a multicenter case-control study were included in the analysis. Adjusted odds ratios (AORs) and 95% confidence intervals (CIs) were estimated using logistic regression. Among married women, those who reported H/HH to be an agricultural worker were at increased risk for bladder cancer as compared to those with H/HH in other occupations, AOR = 1.54, 95% CI [1.09, 2.18]; among unmarried women the risk was not increased, AOR = 0.77, 95% CI [0.45, 1.32]. Nonoccupational exposure to agricultural work, defined as living with an agricultural worker, increased the risk for bladder cancer among married Egyptian women.     

Internal lead and cadmium exposure in 6-year-old children from western and eastern Germany

Lead and cadmium levels in blood and deciduous teeth (shed incisors only) of 6-year-old German children were determined in 1991 in a large epidemiological study carried out in rural and urban areas of western Germany (Duisburg, Essen, Gelsenkirchen, Dortmund, Borken) and eastern Germany (Leipzig, Halle, Magdeburg, Osterburg, Gardelegen, Salzwedel). In total, blood lead and cadmium levels of 2311 German children and tooth lead and cadmium levels of 790 German children were analyzed. Blood lead levels were generally low in all study areas with geometric means between 39.3 g/1 and 50.8 g/l in the western German and between 42.3 g/1 and 68.1 g/l in the eastern German study areas. The mean blood lead level of Turkish children (n = 213) living in the western German study areas was 50.1 g/l and thus 5.6 g/1 higher than the overall geometric mean of the western German children. The higher exposure may be explained by a higher oral uptake from food and different living conditions. These children were excluded from multiple regression analysis because they were all living in the western study areas. The mean tooth lead levels ranged between 1.50 and 1.74 g/g in the western and between 1.51 g/g and 2.72 g/g in the eastern study areas. Thus, they show a distribution pattern similar to blood. Blood and tooth lead levels were higher in urban than in rural areas and higher in the eastern German than in the western German study areas. With regard to the blood and tooth cadmium concentrations, no significant differences between the study areas could be found. The mean cadmium levels in blood ranged between 0.12 g/1 and 0.14 g/l and the mean tooth cadmium concentrations between 20.8 ng/g and 27.8 ng/g. Blood and tooth lead and cadmium levels of the eastern and western German children were thus mainly at a relatively low level in all rural and urban study areas. The study demonstrates and confirms that blood and tooth lead levels are influenced by several demographic, social, and environmental variables. The results indicate that there has been a further significant decrease of lead and cadmium exposure in western German children since our last epidemiological study carried out in the same study areas in 1985/1986.     

The relationship between cadmium exposure or body burden and the concentration of cadmium in blood and urine in man

Summary Cadmium concentration in whole blood (Cd-B) and in urine (Cd-U) has been determined in more than 100 workers exposed to cadmium and in a comparable group of non-exposed workers. The relationship between both parameters and the duration of employment or the intensity of current exposure has been analyzed.In control workers slightly exposed to environmental pollution by cadmium, Cd-U but not Cd-B is significantly correlated with duration of exposure.In exposed workers both Cd-U and Cd-B are correlated with the intensity of exposure but not with the duration of exposure. It is suggested that Cd-B reflects current exposure but that Cd-U may reflect body burden of cadmium when exposure is low (environmental pollution) and current exposure when exposure is high (industrial situations).This work was supported by the Commission des Communautés Européennes and the Fonds National de la Recherche Scientifique.     

House dust as possible route of environmental exposure to cadmium and lead in the adult general population

Contaminated soil particles and food are established routes of exposure. We investigated the relations between biomarkers of exposure to cadmium and lead, and the metal loading rates in house dust in the adult residents of an area with a soil cadmium concentration of > or = 3 mg/kg (n=268) and a reference area (n=205). We determined the metal concentrations in house dust allowed to settle for 3 months in Petri dishes placed in the participants' bedrooms. The continuously distributed vegetable index was the first principal component derived from the metal concentrations in six different vegetables. The biomarkers of exposure (blood cadmium 9.2 vs. 6.2 nmol/L; 24-h urinary cadmium 10.5 vs. 7.0 nmol; blood lead 0.31 vs. 0.24 micromol/L), the loading rates of cadmium and lead in house dust (0.29 vs. 0.12 and 7.52 vs. 3.62 ng/cm(2)/92 days), and the vegetable indexes (0.31 vs. -0.44 and 0.13 vs. -0.29 standardized units) were significantly higher in the contaminated area. A two-fold increase in the metal loading rate in house dust was associated with increases (P<0.001) in blood cadmium (+2.3%), 24-h urinary cadmium (+3.0%), and blood lead (+2.0%), independent of the vegetable index and other covariates. The estimated effect sizes on the biomarkers of internal exposure were three times greater for house dust than vegetables. In conclusion, in the adult population, house dust is potentially an important route of exposure to heavy metals in areas with contaminated soils, and should be incorporated in the assessment of health risks.     

Possible effects of environmental cadmium exposure on kidney function in the Japanese general population

Objectives: To examine whether the current level of environmental exposure to cadmium (Cd) is associated with kidney dysfunction among general populations in Japan. Methods: A nationwide survey was conducted in Japan from 1991 to 1997 at 30 survey sites (with no known environmental heavy metal pollution), by the collection of 24-h food-duplicate samples, peripheral blood specimens and morning spot urine samples. In practice, 607 non-smoking adult women provided these samples. After being wet-ashed, the samples were analyzed for Cd in food duplicates (Cd-F), in blood (Cd-B) and urine (Cd-U) by inductively-coupled plasma mass spectrometry (ICP-MS). Urine samples were also analyzed for α₁-microglobulin (α₁-MG), β₂-microglobulin (β₂-MG) and retinol-binding protein (RBP), creatinine (cr) and specific gravity. Possible tubular dysfunction in association with Cd exposure was examined by simple, multiple and logistic regression analyses, and comparison among three different Cd-dose groups. To minimize the confounding effects of aging, 367 women from 41 to 60 years old were selected and subjected to the same statistical analyses. Results: The analysis of a whole population of 607 women showed that α₁-MG and possibly β₂-MG increased as a function of Cd-F, Cd-B and Cd-U. When the analysis was repeated with the selected population of 367 women aged 41–60, the Cd dose-dependent changes in α₁-MG and β₂-MG became less evident. The distribution of the selected population with α₁-MG above two low cut-off values of >4.9 and >8.4 mg/g cr or with β₂-MG above the lowest cut-off value of >400 μg/g cr, was biased toward the group with higher Cd-Ucr, but such bias was not significant for both α₁-MG and β₂-MG when higher cut-off values were employed. No bias was detected with RBP. Logistic regression analysis with α₁-MG, β₂-MG and RBP (with cut-off values given above) in combination with age, Cd-F, Cd-B and Cd-Ucr gave essentially the same results. Conclusions: The evidence for kidney dysfunction was of borderline significance in the present study population for which geometric mean Cd-F, Cd-B and Cd-U were 24.7 μg/day, 1.76 μg/l, and 3.94 μg/g cr, respectively. The findings might suggest at the same time that the safety margin is small for the Japanese general population regarding environmental Cd exposure. Received: 26 February 1999 / Accepted: 24 July 1999     

Significance of urinary metallothionein in workers exposed to cadmium

Summary Cadmium in blood (Cd-B) and in urine (Cd-U) and metallothionein (Mt-U) and ₂-microglobulin in urine ( ₂m-U) were measured in 94 male Cd workers. The results were examined according to the workers' current exposure to cadmium (group C, n=73, workers currently exposed to Cd; group R, n=21, Cd workers removed from exposure or retired) and according to their renal status (group N, n=66, normal ₂m-U; group 1, n=28, ₂m-U>200 g/g creatinine). The interrelationships between Mt-U, Cd-U, Cd-B and years of cadmium exposure were examined in the various subgroups. The study of the correlations between these variables demonstrates that Mt-U is directly correlated with Cd-U but not with Cd-B or years of Cd exposure. The association between Cd-U and Mt-U is independent of the status of renal function and the intensity of current exposure to cadmium. Under moderate chronic exposure to cadmium, the fraction of Cd-U which is directly influenced by recent exposure (Cd-B) is small in comparison with that influenced by the cadmium body burden.     

Environmental cadmium exposure induces alterations in the urinary metabolic profile of pregnant women

Cadmium (Cd) is a well-recognized, hazardous toxic heavy metal, and the adverse effects of high-level Cd exposure on human health have been well documented. However, little is known about the health effects of low-level environmental Cd exposure on pregnant women. The objective of this study was to assess urinary metabolic alterations in pregnant women exposed to environmental Cd, and to identify informative biomarkers. Urine samples from 246 pregnant women in the first trimester of pregnancy were collected, and urinary Cd concentrations were quantified using inductively coupled plasma mass spectrometry (ICP-MS). Urinary metabolomics was analyzed by ultra-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS). Cd-related metabolic biomarkers were examined by comparing the samples of the first and third tertiles of Cd exposure classifications, using a partial least-squares discriminant (PLS-DA) model. Five putative biomarkers were identified, including L-cystine, L-tyrosine, dityrosine, histamine, and uric acid, all of which were related to oxidative stress and nephrotoxic effects induced by Cd exposure. The results show that low-level environmental Cd exposure could induce metabolite profile alterations in pregnant women, which might be associated with adverse health effects. Our findings provide new insights into the early molecular events following Cd exposure, and may be valuable for the health risk assessment of Cd exposure during pregnancy.     

围产期铅暴露对新生大鼠血铅含量的影响

目的　了解铅通过母体对生长发育期仔代血铅的影响。方法　对不同浓度低水平铅暴露后的大鼠仔代的血铅进行测定。结果　铅可由母体经胎盘和乳汁传递给仔代。结论　胚胎期和哺乳期经胎盘和乳汁“染铅” ,是导致子代铅蓄积的重要原因。     

无锡市某私营铅蓄电池厂铅作业危害分析

目的监测与评价某私营铅蓄电池厂铅作业相关的职业病危害因素,为后续铅作业人员的个人防护和健康监护提供科学依据。方法采用现场调查方法了解该企业职业卫生管理现状,按GBZ159—2004、GBZ／T160．10～2004和GBZ2．1—2007等对工作场所中铅烟、铅尘进行检测和分析并结合职业健康检查分析影响工作人员血铅浓度的潜在因素。结果该企业存在铅烟、铅尘等职业病危害因素;铅烟、铅尘超标率为92．1％,铅作业人员血铅浓度增高比例为77．5％;铅作业人员血铅浓度与工龄、学历、下班前是否沐浴以及铅作业相关卫生知识知晓率有关（均P〈0．05）。结论该私营企业存在明显的铅作业危害,应改善工作环境,加强作业人员健康宣教及健康防护。     

深圳市居民食品中铅、镉的膳食暴露量评估

目的了解近年来深圳市各种食品中铅、镉的污染水平,评估居民的膳食暴露量。方法于2007-2008年通过食品污染物监测网络,随机采集市售的主要食品品种,用电感耦合等离子体质谱法测定各类食品中铅、镉含量,采用点评估的方式,计算居民的实际摄入量水平。根据FAO/WHO食品添加剂联合专家委员会(JECFA)推荐的暂定每周可耐受摄入量(PTW I)及每人每天耐受摄入量(PTD I),评价深圳市居民膳食摄入铅、镉的安全性。结果2007—2008年分别采集900、1 153份食品检测铅含量,铅含量超标率分别为5.67%、5.81%,在各类食品中平均检出值较高的是水产品,分别为0.18、0.21 mg/kg。2007、2008年分别采集831、1 048份食品检测镉含量,镉含量超标率分别为9.39%、8.49%,其中水产品超标率最高,分别为21.57%(66/306)、29.43%(78/265)。2007年和2008年深圳市居民食品中铅每人每天的摄入量分别为63.3和84.2μg,占JECFA推荐的PTD I的29.5%和39.3%。2007和2008年深圳市居民食品中镉每人每天的摄入量分别为46.4和68.0μg,分别占P...     

Occupational and environmental human lead exposure in Brazil

The purpose of this paper is to present a review of data on assessment of exposure and adverse effects due to environmental and occupational lead exposure in Brazil. Epidemiological investigations on children lead exposure around industrial and mining areas have shown that lead contamination is an actual source of concern. Lead in gasoline has been phasing out since the 1980s, and it is now completely discontinued. The last lead mining and lead refining plant was closed in 1995, leaving residual environmental lead contamination which has recently been investigated using a multidisciplinary approach. Moreover, there are hundreds of small battery recycling plants and secondary smelting facilities all over the country, which produce focal urban areas of lead contamination. Current regulatory limits for workplace lead exposure have shown to be inadequate as safety limits according to a few studies carried out lately.     

2009年广州市海珠区餐饮单位大米中铅镉砷污染现状及膳食暴露评估

目的:了解广州市海珠区餐饮行业大米中铅(Pb)、镉(Cd)、砷(As)等重金属污染现状及评估本地居民通过吃米饭摄入铅、镉、砷的情况。方法:抽取辖区内的单位饭堂和餐饮单位的大米样本,采用石墨炉原子吸收法(GFAAS)和原子荧光法(AFS)进行铅、镉、砷等项目的检测。结果:广州市海珠区餐饮行业大米中铅、镉、砷的检出率分别为77.8%、73.1%、97.2%,铅和镉的合格率为94.4%和85.2%,估算居民(平均体重)每周通过大米摄入铅、镉、砷的量为3.2×10-5～0.009、4.9×10-5～0.006、9.8×10-4～0.003 mg.kg-1bw。结论:广州市海珠区餐饮行业大米中铅、镉的含量尚在安全范围,但镉的含量偏高,应引起关注。     

Parental occupational lead exposure and lead concentration of newborn cord blood

The purpose of this study was to determine the influence of parental occupational lead exposure on the lead levels of newborn cord blood in the Taipei area. From September 1984 to June 1985, 5,000 pregnant women voluntarily participated in the study at the Taipei Municipal Maternal and Child Hospital. Each woman was interviewed regarding her and her husband's occupational exposures; 2,948 successfully delivered healthy newborns, and cord blood samples were obtained using Terumo Venoject, and 242 samples were analyzed by graphite furnace atomic absorption spectrometry using an Instrumentation Laboratory 251 instrument. Nine cord blood samples were from newborns with both parents exposed, 26 samples had maternal exposure only, 105 samples had paternal exposure only, and 102 were nonexposed. The results showed that the average lead level of cord blood with both parents exposed was 8.9 +/- 2.9 micrograms%, maternal exposure 9.0 +/- 3.8 micrograms%, paternal exposure 8.3 +/- 3.4 micrograms%, and 6.9 +/- 3.2 micrograms% in the nonexposed group. There were significant differences between the nonexposed and the maternal exposure groups, and also between the nonexposed and paternal exposure groups. All 26 maternal exposures were from lead soldering operations. Multivariate analysis revealed that, after control of father's exposure status, newborn cord blood lead level increased 0.27 micrograms% for each hour the mother spent on lead soldering during a normal working day, thus suggesting that soldering during pregnancy may be hazardous to newborns. Paternal contribution to the cord blood lead levels seemed to be through either working at home with the pregnant mother also at home or bringing work clothes home for laundering.     

Reduced cadmium and lead burden in Japan in the past 10 years

Objective To investigate the current levels of exposure of the Japanese population to cadmium and lead, in comparison with the levels in 1980s. · Design A nation wide survey was conducted in 1991–1994 (the 1990 study) in 19 study sites in Japan as a follow-up to a study conducted in 1979–1983 (the 1980 study). Blood samples and 24-h total food duplicates were collected from women who did not smoke or drink habitually. Methods Blood and food duplicates (after homogenization) were analysed for cadmium (Cd-B and Cd-F, respectively) and lead (Pb-B and Pb-F) by graphite furnace atomic absorption after wet-ashing. · Results Altogether, 467 women volunteered for blood sampling. Of these women, 375 also gave food duplicates. Geometric mean (GM) Cd-B levels in the 1990 study were lower than the corresponding 1980 values in most study sites so that the 1990 grand GM (1.98 ng/ml) for Cd-B was significantly lower than the 1980 GM (3.58 ng/ml). This reduction in Cd-B was related to the reduction in Cd-F (GM for Cd-F was 38.0 g/day in the 1980 study and 30.0 Etg/day in the 1990 study). Dietary intake was almost exclusively the route of Cd burden among the populations studied. Both Pb-B and Pb-F also showed a remarkable reduction, i.e. from 33.9 ng/ml (1980 GM) to 23.2 ng/ml (1990 GM) in the case of Pb-B, and from 32.2 g/day (1980 GM) to 7.1 g/day (1990 GM) in the case of Pb-F. Pb-B, however, did not correlate with Pb-F either in the 1980 or the 1990 study, because Pb intake via inhalation of air remained significant when compared with dietary intake. · Conclusion The Cd burden in Japan has decreased markedly in the past 10 years, although it is still higher than in other countries. The Pb burden has been quite low.     

Blood levels of lead, cadmium, and mercury in the Korean population: Results from the Second Korean National Human Exposure and Bio-monitoring Examination

In Korea, there have been a number of efforts to measure levels of exposure to environmental pollutants among the population. This paper focuses on investigating the distribution of, extent of, and factors influencing the blood levels of lead, cadmium, and mercury in the Korean population, working from data obtained from the Second Korean National Human Exposure and Bio-monitoring Examination. To that end, blood metal concentrations were analyzed from a total of 2369 participants who were 18 years of age and older. The geometric mean concentrations and their 95% confidence intervals of metals in blood were found to be lead, 1.72 μg/dL (95% CI, 1.68-1.76); cadmium, 1.02 μg/L (95% CI, 1.00-1.05); and mercury, 3.80 μg/L (95% CI, 3.66-3.93). Regression analyses indicate that the levels of metals in the blood are mainly influenced by gender, age, and the education levels of the participants. Current smoking status is also found to be a significant factor for increasing both lead and cadmium levels. Although our study, as the first nationwide survey of exposure to environmental pollutants in Korea, has value on its own, it should be expanded and extended in order to provide information on environmental exposure pathways and to watch for changes in the level of exposure to environmental pollutants among the population.     

Further reduction in lead exposure in women in general populations in Japan in the 1990s, and comparison with levels in east and south-east Asia

Objective: The objective of the study was to elucidate the current level of environmental lead (Pb) exposure of women in general population in Japan, where the use of organic Pb in automobile gasoline was phased out from 1973 to reach a zero level early in the 1980s. Methods: A survey was conducted in 27 sites throughout Japan from 1991 to 1997. Five hundred and eighty-eight non-smoking women from the sites offered 24-h food duplicate, peripheral blood, and spot urine samples. Pb in food duplicates (Pb-F), blood (Pb-B), and urine (Pb-U) were analyzed by inductively-coupled plasma mass spectrometry. The results of Pb-F and Pb-B were compared with observations from a study conducted from 1977 to 1981 on 339 women at the same sites. Log-normal distribution was assumed for the evaluation of the results. Results: Geometric means (GMs) of Pb-F, Pb-B, and Pb-U in the 1991–1997 study were 9.0 μg/day, 20.2 μg/l, and 2.18 μg/g creatinine, respectively. The values for Pb-F and Pb-B were substantially lower than the values (32.8 μg/day for Pb-F and 31.7 μg/l for Pb-B) obtained in the 1977–1981 study, which were already low when compared internationally. Cd-U values in the period from 1991 to 1997 also appeared to be among the lowest in the world. Analysis for time-dependent changes in Pb-U was, however, not possible at the time of this study because no values were available for the period from 1977 to 1981. Conclusions: Substantial reductions from 1977–1981 levels in environmental Pb exposure were observed among the study populations in Japan. Current exposure levels appear to be lower than those in other parts of Asia, the USA, and Europe. Received: 16 March 1999 / Accepted: 27 August 1999