A study of urban housing demolitions as sources of lead in ambient dust: demolition practices and exterior dust fall

Demolition of older housing for urban redevelopment purposes benefits communities by removing housing with lead paint and dust hazards and by creating spaces for lead paint-free housing and other community resources. This study was conducted to assess changes, if any, in ambient dust lead levels associated with demolition of blocks of older lead-containing row houses in Baltimore, Maryland (USA). In this article we present results based on dust-fall samples collected from fixed locations within 10 m of three demolition sites. In subsequent reports we will describe dust lead changes on streets, sidewalks, and residential floors within 100 m of the demolition sites. Geometric mean (GM) lead dust-fall rate increased by > 40-fold during demolition to 410 micro g Pb/m2/hr (2,700 micro g Pb/m2 per typical work day) and by > 6-fold during debris removal to 61 micro g Pb/m2/hr (440 micro g Pb/m2 per typical work day). Lead concentrations in dust fall also increased during demolition (GM, 2,600 mg/kg) and debris removal (GM, 1,500 mg/kg) compared with baseline (GM, 950 mg/kg). In the absence of dust-fall standards, the results were compared with the U.S. Environmental Protection Agency's (U.S. EPA's) dust-lead surface loading standard for interior residential floors (40 micro g/ft2, equivalent to 431 micro g/m2); daily lead dust fall during demolition exceeded the U.S. EPA floor standard by 6-fold on average and as much as 81-fold on an individual sample basis. Dust fall is of public health concern because it settles on surfaces and becomes a pathway of ambient lead exposure and a potential pathway of residential exposure via tracking and blowing of exterior dust. The findings highlight the need to minimize demolition lead deposition and to educate urban planners, contractors, health agencies, and the public about lead and other community concerns so that society can maximize the benefits of future demolition activities nationwide.     

A survey of spatially distributed exterior dust lead loadings in New York City

This work documents ambient lead dust deposition values (lead loading) for the boroughs of New York City in 2003-2004. Currently, no regulatory standards exist for exterior concentrations of lead in settled dust. This is in contrast to the clearance and risk assessment standards that exist for interior residential dust. The reported potential for neurobehavioral toxicity and adverse cognitive development in children due to lead exposure prompts public health concerns about undocumented lead sources. Such sources may include settled dust of outdoor origin. Dust sampling throughout the five boroughs of NYC was done from the top horizontal portion of pedestrian traffic control signals (PTCS) at selected street intersections along main thoroughfares. The data (n=214 samples) show that lead in dust varies within each borough with Brooklyn having the highest median concentration (730 μg/ft²), followed in descending order by Staten Island (452 μg/ft²), the Bronx (382 μg/ft²), Queens (198 μg/ft²) and finally, Manhattan (175 μg/ft²). When compared to the HUD/EPA indoor lead in dust standard of 40 μg/ft², our data show that this value is exceeded in 86% of the samples taken. An effort was made to determine the source of the lead in the dust atop of the PTCS. The lead in the dust and the yellow signage paint (which contains lead) were compared using isotopic ratio analysis. Results showed that the lead-based paint chip samples from intact signage did not isotopically match the dust wipe samples taken from the same surface. We know that exterior dust containing lead contributes to interior dust lead loading. Therefore, settled leaded dust in the outdoor environment poses a risk for lead exposure to children living in urban areas, namely, areas with elevated childhood blood lead levels and background lead dust levels from a variety of unidentified sources.     

Effectiveness of lead-hazard control interventions on dust lead loadings: findings from the evaluation of the HUD Lead-Based Paint Hazard Control Grant Program

From 1994 to 1999, the Evaluation of the US Department of Housing and Urban Development Lead-Based Paint Hazard Control Grant Program studied the intervention experiences of over 2800 homes in 11 states in the USA. Each interior intervention was categorized as (in order of increasing intensity) (a) cleaning/spot painting; (b) complete repainting; (c) complete repainting plus window treatments; (d) window abatement plus treatments to other components; (e) abatement of all lead-based paint hazards; or (f) abatement of all lead-based paint. Complete dust testing and environmental data were available for 1034 and 278 dwellings through 12 and 36 months postintervention, respectively. Strategies ranging from complete repainting to window abatement plus other treatments reduced geometric mean preintervention windowsill and floor dust lead loadings up to 36 months postintervention (reductions for complete repainting, from 16 to 5 microg/ft2 on floors and 182 to 88 microg/ft2 on sills; for window abatement plus other treatments, 27-8 microg/ft2 on floors and 570-124 microg/ft2 on sills). Full abatement reduced windowsill and floor loadings from baseline to 12 months postintervention [95-6 microg/ft2 on floors and 518-30 microg/ft2 on sills (data were not available for this strategy at 36 months)]. Window lead-hazard abatement was the most effective measure to reduce dust lead loadings on windows, but this treatment would need to be performed in conjunction with treatments to floors as well as exterior and soil treatments for the most effective control of dust lead on floors.     

An exterior and interior leaded dust deposition survey in New York City: results of a 2-year study

Environmental concentrations of leaded dust were monitored by weekly sample collection of interior and exterior settled dust that had accumulated due to atmospheric deposition. The weekly deposition amounts were measured and the cumulative rates of lead in dust that deposited on a weekly basis over 2 year's time were determined. The sampling analysis revealed that the median values of leaded dust for the interior plate (adjacent to the open window), unsheltered exterior plate, and the sheltered exterior plate were 4.8, 14.2, and 32.3 microg/feet2/week, respectively. The data supports the existence of a continuous source of deposited leaded dust in interior and exterior locations within New York City. Additional data from a control plate (interior plate with the window closed) demonstrate that the source of the interior lead deposition was from exterior (environmental) sources. Because of the ubiquitous nature of lead in our environment and the toxic threat of lead to the cognitive health of children, this data provides a framework for the understanding of environmental exposure to lead and its potential for continuing accumulation within an urban environment.     

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.     

A study of the relationship between ambient lead and blood lead among lead battery workers

 Objective: To examine the relationship between ambient lead levels and blood lead levels and to explore the modifiers of the relationship between ambient lead and blood lead. Method: A cross-sectional study was conducted in two lead battery factories. Blood lead level and ambient lead concentration were measured for each participant concurrently. A structured questionnaire was administered to collect sociodemographic characteristics and occupational history. Design: Biological and personal environmental measurements of 219 lead-exposed workers were analyzed by both simple and multiple linear regression. A regression model was selected for interpretation. Results: A high correlation (r=0.62) between ambient lead (PbA) and blood lead (PbB) was observed. In addition, numerous factors, including age, sex, alcohol consumption, personal hygiene practice and type of lead exposure, were also found to influence blood lead levels. Although PbB was highly correlated with PbA, blood lead level may not be effectively lowered by reducing ambient lead level. Based on the regression coefficients, improvement of hygienic practice was more effective at lowering PbB than reducing ambient lead level. Good hygienic practice may be the preferential way to reduce lead exposure in current conditions. Conclusion: Education of correct work practice may be more important than engineering control in the developing countries to lower blood lead levels in lead battery factories. Received: 28 May 1996/Accepted: 30 August 1996     

Lead dust in Broken Hill homes: effect of remediation on indoor lead levels

This study was undertaken to determine whether home remediation effectively reduced indoor lead levels in Broken Hill, a long-established silver-lead-zinc mining town in outback Australia. A before-after study of the effect of home remediation on indoor lead levels was embedded into a randomized controlled trial of the effectiveness of remediation for reducing elevated blood lead levels in young children. Moist towelettes were used to measure lead loading (microg/m2) on internal windowsills and internal and entry floors of 98 homes; samples were collected before, immediately after, and 2, 4, 6, 8, and 10 months after remediation. Data were log(10) transformed for the analysis. Remediation reduced average indoor lead levels by approximately 50%, and lead levels remained low for the duration of the follow-up period (10 months). The greatest gains were made in homes with the highest initial lead levels; homes with low preremediation lead levels showed little or no benefit. Before remediation, homes located in areas with high soil lead levels or with "poor" dust proofing had higher lead levels than those in areas with lower soil lead levels or with "medium" or "good" dust proofing; these relative differences remained after remediation. There was no evidence that lead loading was reduced by an increased opportunity to become aware of lead issues. We conclude that remediation is an effective strategy for reducing the lead exposure of children living in homes with high indoor lead levels.     

A comparison of mortality related to urban air particles between periods with Asian dust days and without Asian dust days in Seoul, Korea, 2000-2004

Recent papers have reported that Asian dust events have been associated with increased risks of all-cause mortality and rates of respiratory illness. The current study was designed to estimate the relative risk of mortality associated with Asian dust events. We used the daily counts of non-accidental deaths, air pollution and meteorological data in Seoul, Korea from 2000 to 2004. We divided all days during the study period into two groups according to the presence or absence of Asian dust events. For each group, we conducted time-series analysis to estimate the relative risk of total non-accidental death when the concentration of each air pollutant increased by the inter-quartile range (IQR). The average concentrations of every air pollutant on the days without a dust event were lower than those on the days with such an event. We found that the effect sizes of air pollution on daily death rates in the model without Asian dust events were larger than those in the model with Asian dust events, and were statistically significant for all air pollutants (PM(10), CO, NO(2), and SO(2)) except for O(3). Our results suggest that we are likely to underestimate the risk of urban air particles if we analyze the effect size of air pollution on daily mortality during Asian dust events. We hypothesize that the real health effect is much larger than previous results suggested.     

The continuing impact of lead dust on children's blood lead: Comparison of public and private properties in New Orleans

Background

Compared with a maximum collective lead (Pb) estimate of ∼1811 metric tons (MT) in exterior paint on 86,000 New Orleans houses, Pb additives in gasoline were estimated at ∼12,000 MT in New Orleans, yielding ∼9100 MT Pb exhausted as aerosols from vehicles; ∼4850 MT were particles >10 μm and ∼4200 MT were particles <0.25 μm.

Objectives

To evaluate pre-Hurricane Katrina soil Pb and children's blood Pb at public housing and private residential properties in the inner-city compared with the outer city of New Orleans.

Methods

This study includes 224 soil samples from 10 public housing properties and 363 soil samples from residential private properties within an 800 m radius of centroids of public housing census tracts. The Louisiana Childhood Lead Poisoning Prevention Program data from 2000 to 2005 (pre-Hurricane Katrina) was the source for 9807 children's blood Pb (μg/dL) results. Soil and blood Pb data were grouped by public housing census tracts and private residential properties. This study uses Multi-Response Permutation Procedures for statistical analysis.

Results

Brick public properties in the city core had significantly more soil Pb contamination and higher prevalence of elevated children's blood Pb than same-aged brick public properties in the outer areas of the city. The pre-Hurricane Katrina New Orleans concentration of Pb dust in the inner-city soil displayed a median of 438 mg/kg or 3.7 times larger than Pb dust in outlying areas where the median soil Pb was 117 mg/kg (p-value=2.9×10⁻¹⁵). Also, the pre-Hurricane Katrina prevalence of children's blood Pb ≥10 μg/dL was 22.9% within the inner-city compared with 9.1% in the outer areas of New Orleans (p-value=3.4×10⁻⁷⁴).

Conclusions

Comparing the quantities of Pb dust from paint and Pb additives to gasoline, this study supports the later source as a more plausible explanation for the differences in soil Pb and children's blood Pb within public and private housing in the higher traffic congested inner-city core compared with the lower traffic congested outer areas of New Orleans. Similar patterns of environmental Pb dust contamination and childhood Pb exposure are expected in all cities.     

Lead in residential soil and dust in a mining and smelting district in northern Armenia: a pilot study

This pilot study of sources of lead exposure in residential settings was conducted in a mining and smelting district in northern Armenia. Samples of exterior soil and dust and interior house dust were collected in and around apartment buildings in Alaverdi where the country's largest polymetallic smelter is located, and in nearby mining towns of Aghtala and Shamlugh. The NITON XL-723 Multi-Element XRF analyzer was used for lead testing. Lead levels in samples from Alaverdi were higher than those in Shamlugh and Aghtala. In all three towns, the highest lead levels were found in loose exterior dust samples, and lead concentrations in yard soil were higher than those in garden soil. Many soil samples (34%) and the majority of loose dust samples (77%) in Alaverdi exceeded the US Environmental Protection Agency standard of 400 mg/kg for bare soil in children's play areas. In addition, 36% of floor dust samples from apartments in Alaverdi exceeded the US Environmental Protection Agency standard of 40 microg/ft(2) for lead loading in residential floor dust. The Armenian Ministry of Health and other interested agencies are being informed about the findings of the study so that they can consider and develop educational and preventive programs including blood lead screening among sensitive populations.     

A further study of the biological effects of lead on urban and suburban Tokyo school children

Summary There are few reports on lead exposure in children living in the center and the suburbs of large cities. As subjects of epidemiological investigations on the effects of lead exposure in ambient air, school children are very significant in that they have a relatively limited sphere of movement in their daily life. In a previous study the authors compared school children living in the center of Tokyo and those in a suburb of the city and reported that the blood lead levels (PbB) were significantly higher in children living in urban areas [12]. However, it was concluded that further investigation of factors other than ambient air was required to determine the cause of this difference. In the present study, the method used was the same as that of the previous study. However, the areas investigated in the present study were distant from those of the previous study. The results again indicated that the average PbB of school children in the city-center was approximately 2.5–4.8 mg/100 g higher than that of suburban school children, a statistically significant difference. An analysis made on the combined data from both studies according to age revealed that urban school children indicated the highest level among younger urban children, showing a gradual decrease in lead levels as age increased (from 10 to 15 years of age). Suburban children did not show this decline. As a result, it was concluded that these differences in PbB might not be attributable only to lead exposure in ambient air, but to lead exposure from sources such as street dust to which young children are more readily exposed than adults.     

Potential lead on play surfaces: evaluation of the "PLOPS" sampler as a new tool for primary lead prevention

This New Orleans study tested the "potential lead on play surfaces" (PLOPS) sampler, as a tool for measuring the potential lead (Pb) surface loading per area (e.g., microg/ft2) of the soil. The PLOPS is a cylindrical vinyl envelope filled with 1 kg (2.2 lbs) water. A wet wipe, the same type as used for floor wipes, is clipped to the bottom of the cylindrical vinyl envelope and placed on the soil and turned one quarter of a turn and back to obtain a sample. PLOPS samples paired with one conventional soil lead (SL) sample (amount of Pb per mass) up to 2.5 cm (1 in) deep were collected from 25 properties and 67-69 field sites before and after covering them with clean Mississippi River alluvial soil from the Bonnet Carré Spillway (BCS). Permutation methods were used to evaluate results. The correlation was 0.85 between Plops 1 and 2 and the agreement was 0.79 (P-values0.0000001, i.e., extreme). The averages of PLOPS duplicates were used to correlate PLOPS and SL. The simplest mathematical expressions are in the forms y=a+bxc and x=d+eyf, where x is PLOPS and y is SL. The results were:y=-7.42+0.408x0.97 and x=-43.74+24.85y0.69. The agreements were 0.61 and 0.62, respectively (P-value0.0000001). According to the relationship, when the PLOPS measure 40 microg/ft2, the predicted SL is 7.2 mg/kg. Also, when SL measures 400 mg/kg, 1508 microg/ft2 is predicted for PLOPS; therefore, SL concentration underestimates the potential for Pb exposure from the soil surface. The PLOPS tool provides a measurement that is comparable with interior floor wipes because it measures the amount of Pb per area a child is likely to encounter while at play on the soil surface.     

婴幼儿血铅水平及其影响因素

目的　了解婴幼儿的血铅水平及其影响因素。　方法　用石墨炉原子吸收光谱法测定2 6 2例婴幼儿末梢血铅浓度 ,并进行铅中毒影响因素的调查。　结果　婴幼儿血铅算术平均值为0 .4 3μmol/L,范围为 0 .10～ 1.4 5 μmol/L,铅中毒发生率为 37.0 2 % (97/2 6 2 )。不同性别、不同年龄婴幼儿血铅水平及铅中毒发生率差异无显著性 (P>0 .0 5 ) ,各年龄婴幼儿血铅等级分布以 I级最高 ,婴幼儿铅中毒属 II～ III级。饭前不洗手、经常在马路边玩耍、经常看彩色书刊后不洗手、父母职业、住房为 1990年以后建造的是影响婴幼儿血铅水平的因素。　结论　婴幼儿已受到不同程度的铅损伤 ,应引起家长及有关方面的重视     

儿童血铅与胎儿期铅污染的关系

目的了解儿童血铅水平与胎儿期铅污染的关系。方法采集1～5岁儿童手指血和新生儿出生时的脐带血,用原子吸收石墨炉法测定血铅浓度。结果1122例儿童血铅平均为（0.42±0.15）μmol/L,血铅值≥0.483μmol/L的儿童占27.54％;127例新生儿脐带血铅平均为（0.16±0.12）μmol/L,血铅值≥0.483μmol/L的新生儿占0.79％。结论儿童血铅水平高主要是环境污染和生活行为引起,儿童在胎儿期血铅的本底水平已较高,所以预防儿童铅中毒应从孕妇做起。     

970例儿童血铅水平调查分析

目的 :了解福建省宁德市儿童血铅水平及相关危险因素。方法 :对 970例儿童进行血铅水平测定 ,并对个人状况、生活环境等相关因素进行调查。结果 :儿童血铅≥ 10 0 μg/L占 19.5 % ( 1μg/L =0 .0 0 483 μmol/L)。城乡之间无差别 ,年龄较大儿童的血铅值显著高于较小年龄组 ,不良的卫生习惯 ,未补充钙剂的儿童是血铅水平升高的主要危险因素。结论 :农村儿童也存在环境铅中毒的危害 ,良好的卫生习惯、常服钙剂是降低血铅的重要措施     

Characteristics,distribution, source apportionment,and potential health risk assessment of polycyclic aromatic hydrocarbons in urban street dust of Kerman metropolis,Iran

ABSTRACT

In this study, the concentrations of street dust-bound polycyclic aromatic hydrocarbons (PAHs) in Kerman metropolis as a typical arid urban area were determined to investigate the contamination, molecular composition, toxicity, and sources of PAHs. Sixteen individual PAHs on the United States Environmental Protection Agency priority list were analyzed using gas chromatography-mass spectrometry in street dust samples from 30 sites. ∑PAHs ranged between 165 and 5314.7 µg·kg^?1 with a mean of 770.8 µg·kg^?1. The most abundant individual PAHs were fluoranthene, phenanthrene, pyrene, and chrysene, respectively. High molecular weight PAHs (4-6 rings) made 74.8% of ∑PAHs mass and were dominant in all sites. Source apportionment was performed using ring classification, diagnostic ratios, and principal component analysis-multiple linear regression. The results indicated that primary contributors of PAHs in the street dust of Kerman could be liquid fossil fuel combustion, natural gas combustion, and petrogenic sources, accounting for 82.4%, 11.5%, and 6.1%, respectively. The calculated incremental lifetime cancer risk is 8.13 × 10^?4 for children and 6.27 × 10^?4 for adults. Hence, both children and adults in Kerman are potentially exposed to a high carcinogenic risk via ingestion and dermal contact.     

职业接触粉尘及吸烟对死亡影响的前瞻性队列研究

目的 研究接尘和吸烟对死亡的影响。方法 以1989－1992年广州实施并建立的职工职业健康监护档案为基础资料，选年龄≥30岁的接尘工人和无任何粉尘及其他有害物质接触的职工（对照组）61648名为研究对象，进行前瞻性队列研究。结果 （1）队列失访28例，死亡1186例，以恶性肿瘤死亡为主；（2）本队列男性多于女性，年龄35－44岁，主要为工人，中学文化，已婚，率42．2％，饮酒率32．8％；（3）调整相应混杂因素后，全死因、恶性肿瘤和呼吸系疾病死亡接尘者相对危险度（RR）分别为1．24、1．34和1．96，与对照组比较，差异均有显著性（P＜0．01），吸烟者RR分别为1．16、1．37和1．63，与不吸烟者比，前二者差异有显著性（P＜0．01）；既接尘又吸烟者上述相应死因死亡1RR分别为1．48、1．85和3．12，明显高于单纯接尘或单纯吸烟者，差异有显著性（P＜0．01）；（4）接尘对死亡的影响主要表现在职业接触矽尘和木尘。结论 接尘与吸烟均可致死亡危险性增加，并存在协同作用。     

A comparison of household lead exposure assessment methods in an old,urban community

The accurate assessment of lead hazards within the household is critical to the prevention of lead exposure to children living in urban communities. Although dust wipes are currently accepted as the best method of assessing lead hazards, questionnaires and visual inspections are also used. This study evaluates the level of agreement among these three methods of assessment using a sample of 126 women living in old, urban houses. The level of agreement was assessed using the kappa statistic, which adjusts for chance agreement. Overall, the kappa results for both the participant's assessment (questionnaire) and the visual inspector's assessment were low, indicating only slight to moderate agreement with the dust lead wipe levels. Kappas were higher and more consistent for the visual inspector's assessment than for the participant's assessment. These results indicate that visual inspections and participant questionnaires may provide less accurate information regarding lead hazards within the household than dust wipes. Because lead hazard recognition is important in the prevention of lead exposure in children, our data suggest that emphasis should be placed on the measurement of dust lead levels directly in assessing household lead hazards, possibly by teaching women in high-risk neighborhoods to take dust samples themselves.     

接触木尘工人与脱尘工人肺功能的配对研究

为深入研究木尘对接尘工人肺功能的影响，我们按照配对设计原则，对某厂木型车间接触木尘工人与脱离木尘作业工人分别进行了肺通气功能的配对比较分析。结果表明，无论是接尘组工人，还是离尘组工人，其ＦＶＣ、ＦＥＶ１、ＭＭＦ、Ｖ５０与Ｖ２５等肺功能各项指标的实测值，均较对照组明显降低，且多具有显著的统计学意义。累计接尘量与肺功能各指标实测值／预计值百分比间存在着一定的剂量－反应关系，即随着累计接尘量增加肺功能损害加重。多因素分析显示：累计接尘量是致接尘工人肺功能下降的主要因素。提示接尘工人、脱离木尘作业工人肺通气功能的损害与木尘有关。     

Biomonitoring of mercury,cadmium, and lead exposure in Japanese children: a cross-sectional study

Objectives

To measure current Hg, Cd, and Pb exposure in Japanese children, and to estimate dietary intakes of foods responsible for high body burden.

Methods

Blood, hair, and urine samples were collected from 9 to 10-year-old 229 children in Asahikawa and measured for Hg, Cd, and Pb in these matrices. Diet history questionnaire was used to estimate intake of marine foods and other food items. Hg level was measured by cold vapor atomic absorption spectrometry. Cd and Pb levels were determined with inductively coupled plasma mass spectrometry.

Results

Geometric mean (GM) of blood Hg, Cd, and Pb was 4.55 μg/L, 0.34 μg/L, and 0.96 μg/dL, respectively. Urinary Cd level was 0.34 μg/g creatinine (GM) and hair Hg was 1.31 μg/g (GM). Approximately one-third (35 %) of blood samples had Hg level above the U.S. EPA reference dose (RfD; 5.8 μg/L). Hair Hg level exceeded U.S. EPA RfD (1.2 μg/g) in 59 % samples. Children in the upper quartile of blood Hg level had significantly higher intake of large predatory fish species compared to those in the lower quartile of blood Hg.

Conclusions

Those with high blood Hg level may be explained by more frequent intake of big predatory fish. Cd and Pb exposure is generally low among Japanese children. As no safety margin exists for Pb exposure and high exposure to MeHg is noted in Japanese population; periodic biomonitoring and potential health risk assessment should continue in high-risk populations, notably among children.