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1.
Since 1982 the Cree Board of Health and Social Services of James Bay (Quebec, Canada) has taken samples of hair from Cree men and women in the course of the methylmercury (MeHg) surveillance program. As a measure of foetal exposure, samples of hair of the mother are taken at the beginning of pregnancy and shortly after birth (to determine exposure at birth) and a blood sample is taken from the umbilical cord blood of the newborn. Of the 2360 births between 1983 and 1991, 25% had all three samples taken, but there was not a single sample for 25% of the births. From 1983–1991, the concentrations of mercury (Hg) at the time of conception, at the time of birth and in the umbilical cord have decreased progressively. There is no relationship between Hg in the umbilical cord blood and the weight of the newborn. As is to be expected there is a relationship between the maternal hair concentration at birth and umbilical cord blood Hg concentration at birth. The relationship is the following: Hg cord blood = 8.53+.88xHg maternal blood equivalent {r=0.623, 95% CI(r) [0.770, 0.769] p<0.001}.  相似文献   

2.
To obtain the basic information on human exposure to mercury (Hg) due to gold mining activities in Amazon, total mercury (T-Hg) and methylmercury (MeI Ig) were determined for human hair, blood and/or urine samples collected from populations living in gold mining area and fishing villages upstream of the Tapajos River basin. Abnormally high levels of T-Hg were observed in hair and blood from all fishing villages investigated and more than 90% of T-Hg was in the form of MeHg in both samples, whereas in goldrnining area the value were much lower and the %MeHg values varied widely (20–100%) with individuals even in blood samples. Urine from gold shop workers contained Hg mostly in inorganic form at 165μg/g creatinine on the average, with the range of 20 to 450μg/g creatinine. A good correlation between Hg in hair and blood was found in fishing villages and the ratios of hair Hg to blood Hg were very close to 250, generally established for MeHg. T-Hg and inorganic Hg levels in urine from gold shop workers were also significantly correlated with inorganic Hg in blood.  相似文献   

3.
The concentrations of methylmercury (MeHg) in 124 samples of muscle taken from nine species of common sharks of varying sizes and locations along the Florida coast were determined. Muscle MeHg levels averaged 0.88 μg/g (wet sample basis) and ranged from 0.06 to 2.87 μg/g, with 33.1% of the samples exceeding the U.S. Food and Drug Administration's 1 μg/g action level. Differences were found in MeHg concentration by species but not by sex. A positive correlation between MeHg levels and shark size was found such that most sharks larger than approximately 200 cm total length contained MeHg concentrations exceeding the 1 μg/g action level. Fetal sharks contained consistently lower MeHg levels than their mothers. Sharks collected off southern regions of the state contained significantly higher MeHg concentrations than those off the northeast coast. The human health concerns for consumers of Florida shark meat are discussed in relation to these findings.  相似文献   

4.
天津污灌区水稻土壤汞形态特征及其食品安全评估   总被引：5，自引：1，他引：4  
选择天津污水灌溉区作为研究区域,该文的主要研究目的是分析土壤不同形态汞对水稻不同组织中总（THg）和甲基汞MeHg富集的影响以及评估污灌区稻米食用汞暴露风险,并对污灌区土壤溶解与可交换态汞安全阀值进行了初步分析。结果表明,北塘、大沽和北京污灌区稻田土壤THg和MeHg浓度显著高于对照区海河土壤THg浓度。大沽、北京河污灌区和海河土壤汞的形态为残渣态浓度最高,而北塘污灌区为有机结合态浓度最高。由于水稻地上组织中THg浓度受到大气汞浓度影响,各组织中汞浓度在不同污灌区分布规律不同。水稻籽粒的 MeHg 富集系数为1.63～3.70,通过人体每天摄入MeHg量的安全值计算得出土壤溶解与可交换态汞质量分数应低于9.19 ng/g。污灌区食用稻米MeHg暴露对居民健康存在较大风险,人体MeHg每天摄入量超标率达到20.83%。因此,可以对超标土壤进行治理或改变耕作方式来降低土壤污染对人体MeHg暴露造成的影响。  相似文献   

5.
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6.
通过分析广州市区居民消费量较大的7种淡水鱼和5种海水鱼肌肉中甲基汞（MeHg）含量,评估人体通过食鱼摄入MeHg的暴露风险。结果显示,广州市鱼体肌肉中MeHg含量范围为2.39～349μg·kg-1,平均含量为43.4μg·kg-1。不同食性鱼类MeHg含量水平依次为：肉食性〉杂食性〉草食性,处于食物链不同环节解释了这种含量差异。从生长环境来看,海水鱼肌肉的MeHg含量总体上高于淡水鱼。所有鱼中MeHg含量均低于国内外相关标准限值。与国内其他地区商品鱼相比,广州市商品鱼中MeHg含量相当,但明显低于野生鱼。居民通过食鱼摄入的MeHg范围为0.035～0.087μg·kg-1·d-（1bw）,均值为0.050μg·kg-1·d-（1bw）,远低于美国EPA规定的MeHg暴露参考剂量（RfD）值（1.1μg·kg-·1d-1）,也低于WHO和FAO制定的临时性周可承受摄入量（PTWI）（1.6μg·kg-1）。研究结果表明,广州居民食鱼MeHg暴露风险较小,但儿童等敏感人群食用特定鱼类的量和频次要引起一定注意。  相似文献   

7.
In March 1989, The Florida Department of Health and Rehabilitative Services (HRS) issued a Health Advisory recommending the limited consumption of several fish species caught from the Everglades region of South Florida due to elevated methylmercury (MeHg) levels (average 2–3 ppm in fish meat). There were no reports of clinical MeHg poisoning in humans in Florida, although deaths of Florida panthers were attributed to mercury (Hg). poisoning. This study evaluated the extent of MeHg exposure in persons eating contaminated fish in the Everglades region. Populations at risk were identified including sport fishermen, Everglades Residents and subsistence fishermen. Over 1700 individuals were approached; those who had eaten fish or wildlife from the contaminated areas at least once/month for the prior three months were asked to participate. Three hundred and fifty (350) participants completed a brief questionnaire and provided a hair sample for Hg analysis. In 119 (36%) of individuals with levels above the limits of detection, the mean total Hg in hair was 3.62±3.0μg/g [± standard deviation] with a range of 1.28 – 15.57. The most at risk populations identified with respect to Hg levels were Blacks and men. Although the majority of the participants had fished in the Everglades for many years (>15 years), they reported relatively low intake of fish and had low hair Hg levels compared with similar populations in prior studies of other populations at risk. Although 71% of participants knew of the State Health Advisories concerning ingestion of Hg contaminated fish from the Everglades, this did not change their consumption habits. In addition, Blacks, individuals of lower income and of lower education levels were less likely to know about the Health Advisories. Given recent studies of neurologic effects from relatively low in utero MeHg exposure, the continuation of the Mercury Health Advisories and wildlife monitoring in the Everglades are warranted, especially for women of childbearing age and children. However, public education must be targeted for the populations at risk identified in this study in order to reach these populations more effectively.  相似文献   

8.
Health Canada has been collecting data on Inuit and First Nations' methylmercury (MeHg) levels for 25 years. A national overview has been completed and more focussed analyses have now been initiated. This paper deals with two interdependent analytical components: 1) a longitudinal overview of the two most extensively sampled communities in Canada: Grassy Narrows and Whitedog, the residents of which were exposed to ‘point source’ mercury pollution in the 1970's; 2) fetal and post-natal exposure to mercury in these two communities including an outline of the First Nation MeHg child development pilot project in the two communities. A retrospective analysis of Grassy Narrows and Whitedog shows a decreasing MeHg trend in both communities. In Grassy Narrows the average individual annual peak methylmercury level in blood has decreased significantly, from 23.80 ppb (range 1.50–322.90) in 1976 to 7.5 ppb (1.7–46.7) in 1995 (r=-0.65, p<0.001). In Whitedog the average peak has also decreased significantly, from 12.87 ppb (1.50–172.00) in 1976 to 6.1 ppb (1.7–33.3) in 1995 (r=-0.59, p<0.005). However, behind these positive trends is the reality of two communities still suffering the effects of disrupted lifestyles and socio-cultural damage. A number of cord blood samples, maternal blood samples, and samples from women of child-bearing age from these communities have been in the “risk” group (according to the 1990 WHO guidelines). We are therefore now assessing the long term effects of fetal exposure in the communities. Standard clinical examinations in the past failed to prove abnormalities attributable to methylmercury but did not include subtle neuropsychological development tests. Many of the fetally exposed children are now in secondary school. Therefore, we have initiated a pilot project to assess long term effects of methylmercury exposure on the neuropsychological development of these children whose fetal exposure we know. The pilot child development project which was initiated in 1995 in Grassy Narrows and Whitedog, with community support, includes four main components: i) a school records review, looking at attendance, marks, and atypical behaviour; ii) teachers' questionnaires, targeting child behaviour; iii) an in-depth neuropsychological test battery focussing on subtle factors, such as memory, attention, executive functions, perceptual functions and sensory / motor development; and iv) hair sampling, providing current MeHg levels to correlate with results from the previous sampling and findings from the first three components. An overview of progress is given.  相似文献   

9.
Mercury (Hg) contamination of miners, riparian and Indian populations and fish in the Amazon region, due to gold extracting activities, has been studied. Samples of hair, urine, and blood of Indians and prospectors, and hair from riparian fish-eating population and fishes from Madeira river, respectively, were collected and analyzed by Cold Vapor, Atomic Absorption Spectrometry (CV-AAS) techniques. The results obtained showed that the aquatic food chains in the Amazonian ecosystems are contaminated by methylmercury (MeHg), exposing Indians, prospectors and riverines to thr risk of severe health hazard. The highest levels of contamination, based upon hair analysis, were found in riparian of the Madeira river, followed by Cuniã Lake population, Indians (Fresco river) and prospectors, in that order. Blood analysis showed 59% of the samples from Indians and 33% from prospectors with Hg contents above 10 ng mL?1. Analysis of urine, on the other hand, showed 44% of Indians with Hg levels below the detection limit (d.l.), and 30% above 20 ng mL?1, whereas 38% of the prospectors presented Hg concentrations over 20 ng mL?1, and 20% below the d.l. These results prove that prospectors, who hardly ever eat fish but are badly exposed to inorganic Hg vapor, are ocupationally contaminated, while the rest of the populations under survey are exposed to environmental contamination by Hg, through polluted fish ingestion.  相似文献   

10.
Mercury content and speciation were determined in freshwater zooplankton from twelve northern Wisconsin (USA) lakes that spanned gradients of dissolved organic carbon (DOC, 1.6 to 20.9 mg/L) and pH (4.6 to 7.2). MeHg in crustacean taxa ranged from 1 to 479 ng/g dry weight, and from 2 to 45 ng/g in the invertebrate predators. Total Hg in the predators ranged from 20 to 153 ng/g. Although the highest MeHg values were found in the herbivores from high DOC lakes (and the experimentally acidified basin of Little Rock Lake), we observed considerable variation in the relationship between MeHg content of zooplankton and lakewater DOC. Bioconcentration factors (BCF) for both MeHg (3.5 to 7.1 log units) and Hg (3.7 to 5.4 log units) decreased with increasing lake DOC, while pH effects were not as apparent. Bioconcentration of MeHg was higher than Hg indicating that MeHg increases while non-methyl Hg declines in progressively higher trophic levels. Biomagnification factors (BMF) for Hg and MeHg were low relative to BCF. The BMF for crustaceans averaged 0.4 log units for MeHg and ?0.5 log units for Hg, indicating that MeHg increased 2.5-fold from seston to crustacean herbivores, while non-MeHg concentrations declined. Unlike BCF, BMF were not related to DOC or pH. In contrast to studies of vertebrate predators, both BCF and BMF in the invertebrate predatorChaoborus, were lower than those in presumed prey. These observations point toward several complexities in the transport of Hg species in the lower levels of aquatic foodwebs.  相似文献   

11.
Experiments were conducted during a 5 mo period (September 1975 to January 1976) to determine the Pb concentrations in Bangkok streets and blood Pb levels of Bangkok's population. A total of 185 air samples and 222 blood samples was collected and analyzed. Street Pb levels are in the range of 6.16 to 22.48 μg m?3 and blood Pb levels are in the range of 1 to 34 μg (100 g)?1 of whole blood, with an average value of 12.3 μg (100 g)P?1. The effects of various parameters on air and blood Pb levels are discussed in this paper. Air Pb levels are found to be closely related to traffic volume and proximity to the roads. Blood Pb levels are found to increase progressively with age, reaching a saturation value at about 40 yr of age. The average time spent daily on roads by the people and the distance of their residence/workplace from the main road are found to be major parameters, affecting the blood Pb levels. There is no evidence to show that blood and air Pb levels are directly related, at the present ambient exposure levels.  相似文献   

12.
Research on mercury (Hg) distribution and speciation was carried out in Lake Baikal, a large, strong-oligotrophic freshwater reservoir in Siberia, Russia, during June 1992 and march 1993. In summer, total Hg in the water column ranged from 0.14 to 0.77 ng Hg/L, with the highest concentrations observed in the central basin of the lake in surface water samples. Labile inorganic Hg was found to be 7 to 20 % of the total Hg content. Highest total Hg concentrations were found in river waters: up to 2 ng Hg/L. Labile methylmercury (MeHg) concentrations ranged from 2 to 38 pg Hg/L in the water column, with the higher concentrations in the central part of the lake, and showing a slight increase in near bottom waters. Labile MeHg makes up 1 to 15 % of the total Hg content in the water column, with larger fractions in deep waters. The slight increase of the MeHg gradient with depth corresponds with the O2 minimum region. Highest MeHg concentrations were observed in river waters (up to 145 pg Hg/L) and in some bays of the lake (up to 160 pg Hg/L). In these high temperature- and phytoplankton-rich water masses, the MeHg-fraction increased up to 35 % of total Hg. Labile MeHg concentrations in water samples taken in winter in the southern basin (under the ice cover), showed slightly higher concentrations than in summer, possibly due to an early spring bloom. In rainwater, total Hg ranged from 3 to 20 ng Hg/L and MeHg from 0.1 to 0.25 ng Hg/L. In snow, a large fraction of total Hg is bound to particulate matter; concentrations of total Hg ranged from 8 to 60 ng Hg/L and labile MeHg from 0.1 to 0.25 ng Hg/L. Atmospheric Hg was found to be 0.73 to 2.31 ng/m3 as gaseous Hg and 0.005 to 0.02 ng/m3 in its particulate form. Spatial distribution patterns of atmospheric Hg show slightly higher concentrations over the central part of the lake and the Selenga river delta. In winter, atmospheric Hg values (measured in the southern region), ranged from 1.2 to 6.1 ng/m3 as total gaseous Hg and 0.02 to 0.09 ng/m3 as total particulate Hg, and are higher than in summer, probably influenced by coal burning and traffic by the local population. MeHg contents in fish ranged from 20 ng Hg/g dry weight in small Cottocomephorus to 300 ng Hg/g dry weight in pike and trout species, which were caught in organic-rich waters.  相似文献   

13.
The Wisconsin Department of Natural Resources conducted a pilot study during the summer of 1991 to determine the extent of mercury (Hg) exposure in common loons (Gavia immer) breeding in Wisconsin. Loons are at risk to elevated Hg exposure in Wisconsin because they often nest on acidified, low alkalinity lakes. Fish from these lakes bioaccumulate MeHg to a greater extent than biota from neutral pH lakes. Using nightlighting techniques, 35 adult loons were captured on 20 northern Wisconsin lakes (pH=5.0–8.7) in 1991. Blood and feather samples were collected for Hg analysis. The mean Hg content of blood cells collected from adult loons on low pH lakes (pH≤6.3) was significantly greater than the Hg content of adult loons collected on neutral/alkaline pH lakes (pH>-7.0) (F=19.87, P<0.001). There was a highly significant negative linear relationship between adult loon blood cell Hg concentrations and lake pH (r2=0.38, F=15.27, P>0.001); indicating loons nesting on low pH lakes receive greater Hg exposure than loons nesting on neutral pH lakes. The relationship was greater amongst adult males (r2=0.56) than amongst adult females (r2=0.36). Because of this documented exposure, an additional 330 loons were captured 1992-94 on 73 lakes in northern Wisconsin. The Hg exposure of adult and juvenile common loons is being quantified. Individual loons were fitted with unique color-coded leg bands, and the 1992–96 reproductive performance, apnual return rates, and nesting behavior of adult loons with the known Hg exposure is currently being assessed.  相似文献   

14.
Abstract

Although ergosterol is considered to be a suitable indicator of mould growth in cereal grains, there are few reference values available for Scandinavian conditions. We have determined the ergosterol levels in Swedish grain of different origins: cleaned food-grade wheat from a commercial mill, feed-grade cereals (oats and barley) with different odours and cereals (winter wheat, “American wheat”, triticale and rye) from various field trials conducted in south-central Sweden in 1990. Specific objectives were to elucidate the relationships between ergosterol levels and numbers of mould colony forming units (CFU) and between ergosterol and grain odour.

Ergosterol levels in the food-grade wheat ranged between 2.4 and 2.8 μg/g DW, and between 3.0 and 5.6 μg/g DW in the field trial cereals, while values in most of the feed grain samples ranged from 8–15 μg/g DW. The levels agree with other published data for European grains.

A positive correlation was found between numbers of colony-forming units and ergosterol concentration. The degree of correlation was higher when numbers of CFU were determined on dichloran-glycerol 18% agar with a low water activity (aw = 0.95) than on malt extract agar (aw = 0.99). There was no agreement between ergosterol levels and grain odour, since even samples described as having a fresh smell had high ergosterol levels. However, the highest level (33 μg/g DW) was found in a sample with a pronounced musty odour, and the lowest (1.1 μg/g DW) in a sample that smelled as if it had been heat damaged.  相似文献   

15.
A study of total Hg (Hg) and methylmercury (MeHg) was performed in a 40 mgd capacity municipal sewage treatment plant in which elemental Hg was used as a seal in 3 trickling filter center columns. Each seal contains several hundred kg of Hg. The seals have leaked repeatedly over time, prompting the current remediation study and ongoing replacement of the Hg seals with mechanical seals. A mass balance conducted three times while the seals were in place showed that the plant acted as a net source of both Hg and MeHg during normal operation. The average amount of Hg released in sludge plus effluent was 157 g Hg and 0.4g MeHg/d. Of this total, 138 g Hg and 0.3 g MeHg were in excess of influent wastewater, and were contributed by the WTP itself. About 95% of the total Hg was released in sludge, with only 6 to 7 g/d released to the receiving water body. However, on average, about 70% of the MeHg leaving the plant was released to the river. Effluent MeHg concentrations were 4–6 ng/L. The plant components that acted as the major sources of both total and MeHg within the plant were the trickling filters (TFs). Metallic Hg accidentally lost from the center column seals has accumulated in the rock filter media and underbedding of the tricking filters. MeHg production across the TFs was positively related to the Hg concentration in each of the TFs. A substantial fraction of the total Hg but not of MeHg was lost to sludge in each settling step. About 50% of the remaining MeHg appeared to be degraded during the tertiary aeration step.  相似文献   

16.
We studied methylmercury (MeHg) and totalmercury (HgT) in impounded and natural surface waters innorthwestern Minnesota, in settings ranging from agriculturalto undeveloped. In a recently constructed (1995) permanent-pool impoundment, MeHg levels typically increased from inflowto outflow during 1997; this trend broke down from late 1998 toearly 1999. MeHg levels in the outflow reached seasonal maximain mid-summer (maximum of 1.0 ng L-1 in July 1997) andlate-winter (maximum of 6.6 ng L-1 in February 1999), andare comparable to high levels observed in new hydroelectricreservoirs in Canada. Spring and autumn MeHg levels weretypically about 0.1–0.2 ng L-1. Overall, MeHg levels inboth the inflow (a ditch that drains peatlands) and outflowwere significantly higher than in three nearby referencenatural lakes. Eleven older permanent-pool impoundments andsix natural lakes in northwestern Minnesota were sampled fivetimes. The impoundments typically had higher MeHg levels(0.071–8.36 ng L-1) than natural lakes. Five of six lakesMeHg levels typical of uncontaminated lakes (0.014–1.04 ngL-1) with highest levels in late winter, whereas ahypereutrophic lake had high levels (0.37–3.67 ng L-1)with highest levels in mid-summer. Seven temporary-poolimpoundments were sampled during summer high-flow events. Temporary-pool impoundments that retained water for about 10–15days after innundation yielded pronounced increases in MeHgfrom inflow to outflow, in one case reaching 4.6 ng L-1,which was about 2 ng L-1 greater than the mean inflowconcentration during the runoff event.  相似文献   

17.
The occurrence of perchlorate in soybean sprouts (Glycine max L. Merr), water dropwort (Oenanthe stolonifera DC.), and lotus (Nelumbo nucifera Gaertn.) root, which are commonly consumed by people in South Korea, was determined by using an ion chromatograph coupled with a tandem mass spectrometer. For soybean sprouts (11 samples), perchlorate was detected in most (91%) of the samples at various concentrations of up to 78.4 μg/kg dry weight (DW); the mean concentration was 35.2 μg/kg DW. For water dropwort, of the 13 samples examined, four showed concentrations that were above the limit of quantification (LOQ). The mean perchlorate concentration was 20.7 μg/kg DW, and the highest perchlorate value was 39.9 μg/kg DW. Of the six lotus root samples examined, only one exhibited a detectable perchlorate concentration (17.3 μg/kg DW). For the accumulation experiments with artificially contaminated solutions, the concentrations of perchlorate in soybean sprouts gradually increased with the increase of perchlorate concentration in the solution. However, there was a decrease in the bioconcentration factor as the perchlorate concentration in the solution increased.  相似文献   

18.
Malm  O  Calasans  C.F.  Fernandes  A.P.  Bastos  W.R.  Pfeiffer  W.C. 《Water, air, and soil pollution》1997,97(1-2):185-191
Occupational exposure to Hg vapour was investigated in 78 workers during three periods with different temperatures: August 1991, December 1991, and February 1992. Each individual was sampled twice in each period; before and after a six working days period (with a two free days interval). As an attempt to normalise Hg excretion urine was sampled always after a normal 8 hours night sleeping and immediately frozen. Mineralisation was done with acid and oxidant mixture and determination by cold vapour Atomic Absorption Spectrophotometry (Varian VGA-76 and AA-1475). Analytical accuracy was controlled by routine analysis of certified reference material (Seronorm TM trace elements, Nycome As diagnostics Olso - Norway) and all samples were analysed in triplicates. Of a total of 355 samples analysed 13% were over the maximum limit for occupational exposure (50 µg.l-1 or ppb). From the 78 individuals investigated 13% presented average value smaller than 10 ppb; just 8% had the average over 50 ppb; 64% showed averages smaller than 30 ppb; and 28% were between 30 and 50 ppb. Seasonal variation was observed with the highest values in the hottest periods. High variability was observed in the same individual even within an interval of just few days (seven days). No increase of Hg in urine after the six days of exposure was observed when compared with the values after the two free days interval.  相似文献   

19.
This study investigated the spatialand seasonal variations of MeHg concentrations andburdens of different sediments and soils of theTapajós river floodplain, one of the majorclear-water tributaries of the Amazon. The smallfloodplain of the Tapajós is typical of Amazonianfloodplain ecosystems. The studied lakes are borderedby inundated forest (igapó), while floatingmacrophyte mats (Paspalum sp.) develop at themargin of lakes during the flooded season. During theflood, we observed very low MeHg concentrations in theopen water lake sediments (<0.5 ng g-1 d.w or<0.5 μg m-2 cm-1 d.w.) as compared to thesemi-aquatic sediments of the macrophyte zone (0.2–1.4 ng g-1 d.w or 1–3 μg m-2cm-1 d.w.) and the igapó semi-terrestrial soils (0.2–3 ng g-1 d.w or2–12 μg m-2 cm-1 d.w.). The litter horizon fromthe igapó soils showed the highest value of MeHg(4–8 ng g-1 d.w.) representing 0.2–2 μg m-2cm-1 d.w. at the sediment/water interface during theaquatic phase. The inundation had no effect on theconcentrations and burdens of MeHg in the sediment ofthe central part of the lake. The inundation had aclear effect on the methylation of Hg at the surfaceof semi-aquatic shoreline sediments (macrophyte zone)and semi-terrestrial forest soils, where MeHgconcentrations and burdens appeared to be 3 timesgreater following inundation. In all cores, total Hgconcentrations follow those of Fe and Aloxy-hydroxides, whereas the MeHg concentrations arelinked to organic matter quality and quantity. It issuggested that organic matter and inundation controlMeHg production and accumulation at the benthicinterface. These results confirm previousobservations, in the same study area, of net203Hg methylation potentials. The fresh andlabile organic matter in the litter of the igapóforest appears as the most important factor leading tosignificant enrichment of MeHg in these particularterrestrial/aquatic sedimentary environments.  相似文献   

20.
The subcatchments of two tributaries and the headwater mire of the 50 ha Swartberget catchment were studied. Monthly sampling was conducted during 1993 on the two tributaries and at the outlet of a mire. This was complemented by more intensive sampling during spring flood and a rain-driven episode at the end of July. Samples were analyzed for total methylmercury (MeHg), total mercury (Hg-tot) and TOC. The MeHg and TOC content of water were also fractionated into humic and non-humic components. Outputs budgets based on continuous flow monitoring and monthly volume weighted average concentrations of MeHg/ Hg were calculated for the subcatchments of the two tributaries and the mire. There was a pronounced decline in MeHg concentrations at all sampling locations during the spring flood. A clear pattern of the seasonal variation in the MeHg outputs was evident at all three sampling locations. Minimum MeHg concentrations occurred during spring flood and increased during the summer to peak levels in the autumn before tapering off during the winter (except for at the mire). The mire had larger increases in MeHg concentrations during the summer and did not decline during the winter. The warmth and increased soil humidity may promote the biogeochemical processes, including methylation, demethylation which make MeHg available for export by runoff from the soil. Variations in Hg-tot concentrations were differed from MeHg in streams that there were increases in Hg-tot concentrations with flow during both spring flood and the July rain event in runoff from the forested tributaries. The highest outputs of both humic and non-humic MeHg occurred during summer from all subcatchments. Those high outputs extended into the autumn at the mire. The largest monthly output of Hg-tot was during the spring flood period and the next largest was during the period of summer rainfall. Despite the similarity in mineralogy and atmospheric deposition on the two tributary subcatchments, there was ca 30% larger ouput of MeHg per unit area from the tributary which had deeper riparian peats. The output of Hg-tot, however, was higher on the catchment with the shallower riparian peats. The difference in the geometry of the riparian zone may contribute to these differences in output. The annual output concentrations at the mire outlet of MeHg was 0.65 ng /L and of Hg-tot was 4.04 ng/L. In the main tributary MeHg was 0.42 ng/L and Hg-tot was 3.64 ng/L. In the Västrabäcken tributary, the mean MeHg concerntration was 0.25 ng/L and the Hg-tot concerntration was 4.02 ng/L. Among the three subcatchments the largest annual output fluxes of MeHg were from the mire, 0.16 g/km2*yr, the next from Kallkällbäcken below the mire, 0.12 g/km2*yr, and the lowest from Västrabäcken, 0.08 g/km2*yr.  相似文献   

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