Identifying and managing adverse environmental health effects: 3. Lead exposure

LEAD LEVELS IN NORTH AMERICAN CHILDREN AND ADULTS have declined in the past 3 decades, but lead persists in the environment in lead paint, old plumbing and contaminated soil. There are also a number of occupations and hobbies that carry a high risk of lead exposure. There is no evidence for a threshold below which lead has no adverse health effects. Blood lead levels previously considered safe are now known to cause subtle, chronic health effects. The health effects of lead exposure include developmental neurotoxicity, reproductive dysfunction and toxicity to the kidneys, blood and endocrine systems. Most lead exposures are preventable, and diagnosing lead poisoning is relatively simple compared with diagnosing health effects of exposures to other environmental toxins. Accurate assessment of lead poisoning requires specific knowledge of the sources, high-risk groups and relevant laboratory tests. In this article we review the multiple, systemic toxic effects of lead and provide current information on groups at risk, prevention, diagnosis and clinical treatment. We illustrate how the CH²OPD² mnemonic (Community, Home, Hobbies, Occupation, Personal habits, Diet and Drugs) and specific screening questions are useful tools for physicians to quickly obtain an environmental exposure history and identify patients at high risk of lead exposure. By applying effective primary prevention, case-finding and treatment interventions for lead exposure, both the individual patient and the larger community reap the benefits of better health.CaseA previously healthy 2-year-old girl and her mother visit their family physician because of the daughter''s 2-month history of intermittent complaints of a mild “tummy ache.” There is no associated vomiting, weight loss, or change in appetite, bowels or diet. There are no abnormal findings on physical examination. When asked about symptom onset the mother reports that it began shortly after the family started to renovate their kitchen. They live in an old farmhouse on the outskirts of town and drink water from a drilled well on the property. The physician decides to take an environmental exposure history using the CH²OPD² mnemonic (Community, Home, Hobbies, Occupation, Personal habits, Diet and Drugs; for children, the occupation question refers to workplace contaminants brought into the child''s environment).¹ The child''s exposure history (Open in a separate windowQuestions surrounding this case: Is the family at risk of health effects from lead exposure? Who else might be at risk? Are other laboratory tests indicated? Where can the physician get advice on the significance of the family''s blood lead levels? How should this case of lead exposure be treated?To some extent lead is one of the small success stories of environmental health. The association of lead poisoning with cognitive impairment is well established² and has resulted in the removal of lead from gasoline, paint and food cans. Despite these preventive measures, however, silent, low-level lead exposure continues to present a problem for many communities and populations. In 1997, data from the US National Health and Nutrition Examination Surveys showed that 4.4% of children in the United States had elevated blood lead levels.³ Black children living in older housing, children living in metropolitan areas with populations of 1 million or more and poor children living in older housing were at highest risk of exposure.³In Canada children living near a point-source smelter in the South Riverdale area of Toronto were tested in 1973 and found to have an unusually high mean lead level (1.34 μmol/L).⁴ Canada''s Federal–Provincial Committee on Environmental and Occupational Health suggested in 1994 that 5%–10% of Canadian children living in urban areas have blood lead levels exceeding 0.48 μmol/L, even though they are not exposed to point sources.⁵ The Ontario government estimated in 1994 that 4% of children in the province still had blood lead levels above 0.48 μmol/L;⁶ a 1992 study found that the mean level in Ontario children had fallen from 0.91 μmol/L in 1972 to 0.29 μmol/L in 1988.⁷ A study of Vancouver children using blood lead levels collected in 1989 found that 8% had elevated levels (mean 0.29 μmol/L).⁸ A later study of the children living in Trail, BC, the site of a lead and zinc smelter, demonstrated that 50% had an elevated blood lead level.⁹     

Chromosome aberrations, micronuclei and sister-chromatid exchanges in blood lymphocytes after occupational exposure to low levels of styrene

Chromosome aberrations, micronuclei and sister-chromatid exchanges were analysed in blood lymphocytes of 21 reinforced plastic workers, exposed to styrene from 1 to 25 years, and 21 control persons. Occupational hygienic measurements showed personal exposure to styrene to range from 34 to 263 mg/m3 air, the average was 98 mg/m3. Urinary mandelic acid levels of the workers varied from below detection limit to 7 mM/1 l urine. No increase was detected in the frequency of any of the cytogenetic endpoints studied. No correlations between the number of aberrations, micronuclei or SCEs on one hand and the extent or duration of exposure to styrene on the other could be detected.     

High blood lead level among garage workers in Bangkok, public concern is necessary

Lead is an important toxic metal agent found in many industrial processes in the present day. Lead exposure must be of particular concern because of ongoing exposure to thousands of workers in the industrial plants and recent research indicating that asymptomatic lead exposure can result in chronic toxicity manifestations. Therefore, determination and control lead exposure among the risk workers is very necessary. Like other developing countries, lead pollution becomes an important public health problem of Thailand, especially for the big cities as Bangkok but relatively few of these countries have introduced policies and regulations for significantly combating the problem. We set this pilot study to determine the blood lead levels by anodic stripping volammetry (ASV) method as a marker for lead exposure among the occupational exposed and control subjects. Totally 89 subjects, 20 control subjects and 69 garage workers (52 mechanics and 17 dye sprayers), as the representatives of occupational exposed subjects, were included into this preliminary study. The mean blood lead level in the control group was 0.32±0.07 mol/l. The mean blood lead level in the mechanics group was 0.42±0.13 mol/l. The mean blood lead level in the dye sprayers was 0.58±0.07 mol/l. Significant higher blood lead levels among the mechanics and dye sprayer groups were observed (P<0.05). Based on this study, the considerations for prevention of possibly exposure to lead among the high-risk workers as public health policies was recommended.     

Biological monitoring,by in vivo XRF measurements,of occupational exposure to lead,cadmium, and mercury

In vivo X-ray fluorescence (XRF) techniques were used for biological monitoring of lead, cadmium, and mercury. Lead accumulates in bone, the level of which may thus be used for monitoring of exposure. However, there was no close association between lead levels in bone and exposure time, partly because of differences in exposure patterns and partly, probably, because of variations in the toxicokinetics of lead. There are at least two separate bone lead compartments. The average over-all half-time is probably 5–10 yr. The finger bone level may be an index of the lead status of the total skeleton. In lead workers, the mobilization of bone lead causes an “internal” lead exposure and affects the blood lead level considerably. In cadmium workers, in vivo XRF is a sensitive and risk-free method for assessment of accumulation in kidney cortex, the critical tissue as to toxic effects; workers displayed increased levels. However, there was no clear association with duration and intensity of exposure, cadmium levels in urine, or microglobulinuria. Determinations of kidney cadmium may add important information on the state of accumulation and, thus, risk of kidney damage. Workers exposed to elemental mercury vapor, as well as fishermen exposed to methyl mercury, had mercury levels in bone below the detection limit of the XRF method.     

Plasma and erythrocyte lipid peroxide levels in workers with occupational exposure to lead

The plasma and erythrocyte lipid peroxide levels were measured in a group of male subjects occupationally exposed to lead for an average period of 17 yr, and compared to those from an age-matched control group living in the same city in a similar socioeconomical environment. The blood lead and plasma zinc levels were measured by atomic absorption spectroscopy. The plasma and erythrocyte lipid peroxide levels were established by the malondialdehyde determination method. Significant differences were found in the blood lead levels in lead-exposed workers, 15.00±10.15 μg/dL as compared to controls, 2.37±0.89 μg/dL. The plasma (2.67±0.69 μM) and erythrocyte (27.53±6.28 nmol/g Hb) lipid peroxide levels in workers with occupational exposure to lead were significantly higher than controls, 1.23±0.61 μM and 14.35±2.08 nmol/g Hb, respectively. There were no significant differences of the zinc levels in both groups. The blood lead levels had a statistically significant positive correlation with age and with duration of exposure in both groups, but showed no relationship to the corresponding blood zinc levels. The results presented in this study indicate that the increase of plasma and erythrocyte lipid peroxide levels in workers exposed to lead may be related to the lead concentration, age and duration of exposure.     

Lead concentrations in cortical and trabecular bones in deceased smelter workers

The aim of the study was to compare bone lead concentrations in cortical and trabecular bones in long-term exposed primary copper and lead smelter workers, and to relate the measured concentrations to the previous lead exposure of the workers. Lead concentrations in seven bones (trabecular: sternum, vertebrae, iliac crest, rib; cortical: femur, left forefinger, and temporal bone) were determined by electrothermal atomic absorption spectrometry in 32 male, long-term exposed copper and lead smelter workers, and compared with levels in 10 male occupationally unexposed reference persons. A time-integrated blood lead index (cumulative blood lead index, CBLI) was calculated for each worker. The lead levels in the seven studied bones were all significantly higher in active and retired lead workers as compared with the reference group (p相似文献   

Exposure assessment of benzene in Thai workers, DNA-repair capacity and influence of genetic polymorphisms

Exposure to benzene can cause DNA damage and the subsequent development of cancer. In this study, study subjects were 31 laboratory workers at a petrochemical factory and 31 gasoline service attendants. Control subjects were 34 workers from a mail sorting service center. Occupational exposures to benzene were assessed using biomarkers of exposure in blood and urine. Induction of DNA-repair capacity was assessed as a biomarker of early effect. The effects of polymorphisms in a metabolizing gene (CYP2E1), in detoxification genes (NQO1 and GSTT1), and in a DNA-repair gene (XRCC1, codon 399) on biomarker levels were evaluated. The mean individual benzene exposure of laboratory workers (24.40+/-5.82 ppb) and that of gasoline service attendants (112.41+/-13.92 ppb) were significantly higher than in controls (1.39+/-0.17 ppb, p<0.001). Blood benzene levels of laboratory workers (169.12+/-30.60 ppt) and gasoline service attendants (483.46+/-59.62 ppt) were significantly higher than those of the controls (43.30+/-4.89 ppt, p<0.001). Trans,trans-muconic acid levels in post-shift urine samples collected from laboratory workers (0.14+/-0.02 mg/g creatinine) and gasoline service attendants (0.20+/-0.02 mg/g creatinine) were significantly higher than in urine samples of controls (0.04+/-0.01 mg/g creatinine, p<0.001). The level of benzene exposure was correlated with blood benzene levels (R2=0.65, p<0.01) and post-shift urinary trans,trans-muconic acid concentrations (R2=0.49, p<0.01). As a biomarker of early effect, DNA-repair capacity was assessed by use of the cytogenetic challenge assay, i.e., chromosomal aberrations in peripheral lymphocytes were assessed after challenging blood cultures with 1 Gy gamma radiation. A significantly lower DNA-repair capacity--determined as dicentrics in laboratory workers (0.17 per metaphase cell) and in gasoline service attendants (0.19 per metaphase cell) compared with controls (0.12 per metaphase cell, p<0.001)--was observed. The frequency of deletions in laboratory workers (0.22 per metaphase cell) and gasoline service attendants (0.39 per metaphase cell) were significantly higher than in control workers (0.16 per metaphase cell, p<0.01 and p<0.001, respectively). An increase in radiation-induced dicentrics and deletions indicate a lower DNA-repair capacity in benzene-exposed workers. The influence of genetic polymorphisms on the biomarkers was assessed. Benzene-exposed workers who carried CYP2E1*1/*5 or *5/*5 genotypes excreted slightly higher levels of trans,trans-muconic acid than workers who carried the CYP2E1*1/*1 genotype. In this study, NQO1 and GSTT1 genotypes did not have any effect on the levels of trans,trans-muconic acid. In the case of XRCC1, laboratory workers with 399Arg/Gln or Gln/Gln had a lower DNA-repair capacity--measured as radiation-induced frequency of dicentrics and deletions--than those with the 399Arg/Arg genotype (p<0.01). Our results show that biomarkers of internal dose and early biological effect in people occupationally exposed to benzene are influenced by genetic polymorphisms in susceptibility genes.     

Absence of relation between sick leave caused by musculoskeletal disorders and exposure to magnetic fields in an aluminum plant

This is a study of the relationship between occupational exposure to magnetic fields in pot rooms and occurrence of sick leave caused by musculoskeletal disorders. The average exposure to static magnetic fields was 8 mT in the pot rooms. Ripple fields were recorded as well. A cohort of 342 exposed workers and 222 unexposed workers from the same electrolysis plant was retrospectively followed for 5 years. The reference group had a type of work similar to the exposed group except for the exposure to magnetic fields. The occurrence of sick leave and the diagnoses causing the sick leave were obtained from the Occupational Health Care Unit: these data were stored in their computer files. The data were complete. No relationship between the occurrence of sick leave caused by musculoskeletal disorders and exposure to magnetic fields was found. This was the case for both the annual number of periods of sick leave and the total number of days with sick leave. The results must be interpreted with caution due to limitations in the design and available data. Also, static magnetic fields constituted the major exposure, and the results may be different when related to work in other types of magnetic-field exposure. © 1996 Wiley-Liss, Inc.     

Is lead in tap water still a public health problem? An observational study in Glasgow.

OBJECTIVE: To assess the relation between tap water lead and maternal blood lead concentrations and assess the exposure of infants to lead in tap water in a water supply area subjected to maximal water treatment to reduce plumbosolvency. DESIGN: Postal questionnaire survey and collection of kettle water from a representative sample of mothers; blood and further water samples were collected in a random sample of households and households with raised water lead concentrations. SETTING: Loch Katrine water supply area, Glasgow. SUBJECTS: 1812 mothers with a live infant born between October 1991 and September 1992. Blood lead concentrations were measured in 342 mothers. MAIN OUTCOME MEASURES: Mean geometric blood lead concentrations and the prevalence of raised tap water lead concentration. RESULTS: 17% of households had water lead concentration of 10 micrograms/l (48.3 nmol/l) or more in 1993 compared with 49% of households in 1981. Tap water lead remained the main correlate or raised maternal blood lead concentrations and accounted for 62% and 76% of cases of maternal blood lead concentrations above 5 and 10 micrograms/dl (0.24 and 0.48 mumol/l) respectively. The geometric mean maternal blood lead concentration was 3.65 micrograms/dl (0.18 mumol/l) in a random sample of mothers and 3.16 micrograms/dl (0.15 mumol/l) in mothers whose tap water lead concentrations were consistently below 2 micrograms/l (9.7 nmol/l). No mother in the study had a blood lead concentration above 25 micrograms/dl (1.21 mumol/l). An estimated 13% of infants were exposed via bottle feeds to tap water lead concentrations exceeding the World Health Organisation''s guideline of 10 micrograms/l (48.3 nmol/l). CONCLUSIONS: Tap water lead and maternal blood led concentrations in the Loch Katrine water supply area have fallen substantially since the early 1980s. Maternal blood lead concentrations are well within limits currently considered safe for human health. Tap water lead is still a public health problem in relation to the lead exposure of bottle fed infants.     

Use of the IEUBK Model for Determination of Exposure Routes in View of Site Remediation

The Integrated Exposure Uptake Biokinetic (IEUBK) model is frequently used to estimate blood lead concentrations of children exposed to lead. Simulations with the IEUBK model were run to estimate the blood lead concentration in children living in the vicinity of a non-ferrous plant, situated in Hoboken, Belgium. Concentrations in soil ranged from 59–2425 mg Pb/kg dm, average concentrations in house dust ranged from 234–73394 mg Pb/kg dm. Measured blood lead concentrations in children aged 2–7 years were between 3 and 35 μ g/dl. Exposure sources were indoor dust in the house and the school, outdoor dust and soil in the home surrounding and at the school's playground, and suspended dust in the air. Soil ingestion values and lead exposure from food were changed to Flemish values. The model was able to predict the measured blood lead concentrations adequately except for the lowest exposure group. Predictions showed a systematic overestimation. Analysis of the data revealed that the neighbourhood's school is an important source of exposure to lead; indoor house dust dominates exposure for children going to school outside the area, because of the high concentrations of lead in indoor dust (3 to 5 times higher than in outdoor soil).     

DNA-protein crosslinks in peripheral lymphocytes of individuals exposed to hexavalent chromium compounds

Abstract

DNA-protein crosslinks were measured in peripheral blood lymphocytes of chrome-platers and controls from Bulgaria in order to evaluate a genotoxic effect of human exposure to carcinogenic Cr(VI) compounds. Chrome-platers and most of the unexposed controls were from the industrial city of Jambol; some additional controls were recruited from the seaside town of Burgas. The chrome-platers had significantly elevated levels of chromium in pre- and post-shift urine, erythrocytes and lymphocytes compared with the control subjects. The largest differences between the two groups were found in erythrocyte chromium concentrations which are considered to be indicative of Cr(VI) exposure. Despite the significant differences in internal chromium doses, levels of DNA-protein crosslinks were not significantly different between the combined controls and exposed workers. Individual DNA-protein crosslinks, however, correlated strongly with chromium in erythrocytes at low and moderate doses but at high exposures, such as among the majority of chrome-platers, these DNA adducts were saturated at maximum levels. The saturation of DNA-protein crosslinks seems to occur at 7–8 μg I-¹ chromium in erythrocytes whereas a mean erythrocyte chromium among the chrome platers was as high as 22.8 μg l^?1. Occupationally unexposed subjects exhibited a significant variability with respect to the erythrocyte chromium concentration, however erythrocyte chromium levels correlated closely with DNA-protein crosslinks in lymphocytes. The controls from Jambol had higher chromium concentrations in erythrocytes and elevated levels of DNA-protein crosslinks compared with Burgas controls. Occupational exposure to formaldehyde among furniture factory workers did not change levels of DNA-protein crosslinks in peripheral lymphocytes. DNA-protein crosslink measurements showed a low intraindividual variability and their levels among both controls and exposed indivduals were not affected by smoking, age or weight.     

Arsenic exposure levels of petrochemical workers in three workplace settings in Rayong Province,Thailand

Background: Crude oil and natural gas are often contaminated with arsenic. As a carcinogen, arsenic contamination in the workplace is of concern, particularly when urinary arsenic levels are higher than the standard. The aim of this study was to identify exposure sources of arsenic among petrochemical workers. Methods: A total of 188 operators and 30 office workers participated in the study. Ninety-three workplace air samples, three main meals in five consecutive days, and drinking water were collected from each participant. Urine was collected at the end of the day after the last food sample was collected from each subject. Urine samples where arsenic concentration exceeded 100 mg/L were further analyzed to identify species. Results: The average arsenic concentrations in operators' and office workers' food and urine were 0.55 ± 1.00 and 0.49 ± 0.67 mg/kg; and 76.43 ± 107.36 and 149.92 ± 200.28 mg/L, respectively. The arsenic concentrations in air and water were well below their standards. The urinary arsenic correlated well with arsenic in the food but not in the air and water. Conclusion: Occupational exposure to arsenic among operators and office workers was lower than 1% TLV (Threshold limit value) and did not differ significantly. The major source of arsenic exposure Q2 was food.     

The Effect of Occupational Lead Exposure on Blood Levels of Zinc, Iron, Copper, Selenium and Related Proteins

The study objective was to evaluate the effect of occupational lead exposure on blood concentrations of zinc, iron, copper, selenium and proteins related to them, such as transferrin, caeruloplasmin and haptoglobin. The examined group consisted of 192 healthy male employees of zinc?Clead works. By the degree of lead exposure, the exposed group was subdivided into three subgroups. The control group was composed of 73 healthy male administrative workers. The markers of lead exposure (blood levels of lead and zinc protoporphyrin) were significantly elevated in the exposed group compared with the control group. Additionally, concentrations of copper and caeruloplasmin were raised. The significant increase in haptoglobin level was observed only in the low exposure group. Selenium levels were significantly decreased, whereas iron, zinc and transferrin levels were unchanged in the exposed group compared with the control group. There were positive correlations between the lead toxicity parameters and the copper and caeruloplasmin levels. In conclusion, the effect of occupational exposure to lead on the metabolism of trace metals appears to be limited. However, significant associations between lead exposure and levels of copper and selenium were shown. Changed levels of positive acute-phase proteins, such as caeruloplasmin and haptoglobin, were also observed.     

Effect of lead,calcium, iron,zinc, copper and magnesium on anemia in children with BLLs ≥ 100 μg/L

ObjectiveAdverse effects of lead exposure on children's health have been demonstrated. While studies have examined the relationship between iron status and low-level lead exposure in children with blood lead levels (BLLs) < 100 μg/L, few have investigated the association between blood lead and other trace elements and anemia in children with BLLs ≥ 100 μg/L. This study aimed to assess the levels of lead, iron, copper, zinc, magnesium, and calcium in children aged 0–14 with BLLs≥ 100 μg/L between 2009 and 2021, and to examine the relationship between blood lead, trace elements and anemia.MethodsA total of 11,541 children with BLLs ≥ 100 μg/L were included in this study. Venous blood samples were collected to measure blood lead levels, hemoglobin levels, and trace element levels. According to the World Health Organization standard, outpatients with hemoglobin levels < 110 g / L were defined as having anemia.ResultsThe study results found that high BLLs and blood calcium had a negative influence on Hb with odds ratios (95% confidence interval) of 1.411(1.208, 1.649) and 1.219(1.043, 1.424). High blood iron had a positive influence on Hb with odds ratios of 0.421(0.355, 0.499).ConclusionThe results suggest that the risk of anemia rose significantly with higher BLLs, blood copper, and blood calcium levels, and decreases considerably with higher blood iron levels.     

Occupational exposure to genotoxic agents.

Millions of workers in the United States are potentially exposed each year to hazardous chemicals, dusts, or fibers in occupational settings. Some of these agents are genotoxic and may cause genetic alterations in the somatic or germ cells of exposed workers. Such alterations, if they occur in proto-oncogenes or tumor suppressor genes, which are involved in controlling cell growth or differentiation, may lead to the development of cancer. Genetic alterations in germ cells may also lead to reproductive failure or genetic disorders in subsequent generations. It has been estimated that occupational exposure accounts for 4% of all human cancers and up to 30% of cancer among blue-collar workers. Approximately 20,000 cancer deaths each year are attributable to occupational exposure in the United States. Occupational cancer and reproductive abnormalities have been listed on the National Occupational Research Agenda master list of research priorities as major occupational diseases and injuries.     

Effect of Soil Dose on Bioavailability of Lead from Mining Waste Soil in Rats

Abstract

The purpose of this study was to determine the extent of absorption of lead (Pb) in mining waste soil from Butte, Montana. It is the first study to fully investigate the bioavailability of lead in soils containing mine waste using a soil dose response approach. Young 7–8 week-old male and female Sprague-Dawley rats (5 animals/sex/group) were given mining waste soil [810 ppm lead (Test Soil I) or 3,908 ppm lead (Test Soil III)] mixed in a purified diet (AIN—76?) at four different dose levels (0.2, 0.5, 2 and 5% dietary soil) for 30 consecutive days. The test soil dose levels at 2 and 5% were chosen to bracket a pica-for-soil child's soil exposure levels. A pica-for-soil child is a young child who eats large quantities of soil (10 g day^?1). Standard groups included untreated controls and dosed feed soluble lead acetate groups (1, 10, 25, 100 and 250 μg Pb g^?1 feed). The concentrations of lead acetate were chosen to bracket the test soil dose levels of lead. Liver, blood and femur, representing the three compartments in which lead is distributed in the body, were analyzed for total lead concentration using graphite furnace atomic absorption spectroscopy. Clinical signs, body weight, food consumption and liver weights for treated and standard groups were similar to control. Tissue lead concentrations from test soil animals were significantly lower than the tissue concentrations for the dosed feed lead acetate group. Group mean whole blood, bone and liver lead concentrations increased with increasing dose levels for most treatment groups. The increases in blood, bone and liver lead concentrations were not proportional with increasing dose levels and plateaued at the high dose levels. Relative percent bioavailability values, based on dosed feed soluble lead as the standard, were independent of the two different test soils, dose levels or sex, and only slightly dependent on the tissue (blood > bone, liver). Overall relative percent bioavailability values were 20% based on the blood data; 9% based on the bone data; and 8% based on the liver data (2 and 5% dose levels only). The results of this study will provide the scientific validity needed to determine the significance of lead exposure from Butte soils in assessing human health risks as part of the Superfund Remedial Investigation/Feasibility Study process.     

A Dietary-Wide Association Study (DWAS) of Environmental Metal Exposure in US Children and Adults

Background

A growing body of evidence suggests that exposure to toxic metals occurs through diet but few studies have comprehensively examined dietary sources of exposure in US populations.

Purpose

Our goal was to perform a novel dietary-wide association study (DWAS) to identify specific dietary sources of lead, cadmium, mercury, and arsenic exposure in US children and adults.

Methods

We combined data from the National Health and Nutrition Examination Survey with data from the US Department of Agriculture''s Food Intakes Converted to Retail Commodities Database to examine associations between 49 different foods and environmental metal exposure. Using blood and urinary biomarkers for lead, cadmium, mercury, and arsenic, we compared sources of dietary exposure among children to that of adults.

Results

Diet accounted for more of the variation in mercury and arsenic than lead and cadmium. For instance we estimate 4.5% of the variation of mercury among children and 10.5% among adults is explained by diet. We identified a previously unrecognized association between rice consumption and mercury in a US study population – adjusted for other dietary sources such as seafood, an increase of 10 g/day of rice consumption was associated with a 4.8% (95% CI: 3.6, 5.2) increase in blood mercury concentration. Associations between diet and metal exposure were similar among children and adults, and we recapitulated other known dietary sources of exposure.

Conclusion

Utilizing this combination of data sources, this approach has the potential to identify and monitor dietary sources of metal exposure in the US population.     

Low level environmental lead exposure--a continuing challenge

The current threshold for lead toxicity, defined as a blood lead level of 10 mug/dL, was adopted by the United States (US) Centers for Disease Control and Prevention (CDC) in 1991 and the World Health Organization in 1995. Since that time, adverse health outcomes at blood lead levels below this threshold have been well demonstrated. Most concern probably relates to children of pre-school age; an international pooled analysis has demonstrated lead-associated intellectual deficits at blood lead levels well below 10 mug/dL. In the case of adults, several convincing population studies have shown a positive association between blood lead and risk of death. The largest such study compared mortality information from participants with blood lead levels in the highest third of the blood lead distribution (3.6 mug/dL or greater) with those in the lowest third (less than 1.9 mug/dL). After adjustment for potential confounders, estimates of the excess risk were 25% for all cause mortality and 55% for cardiovascular mortality. The adverse consequences of lead exposure have no discernible blood lead threshold, implying there is no safety margin at existing exposure levels. Despite marked declines in population mean blood lead levels since 1980, low level environmental lead exposure remains a significant public health concern.     

Occupational Hearing Loss among Chinese Municipal Solid Waste Landfill Workers: A Cross-Sectional Study

Background

Occupational hearing loss is an increasingly prevalent occupational condition worldwide, and has been reported to occur in a wide range of workplaces; however, its prevalence among workers from municipal solid waste landfills (MSWLs) remains less clear. This study aimed to investigate the occupational hearing loss among Chinese MSWL workers.

Methods

A cross-sectional study of 247 workers from 4 Chinese MSWLs was conducted. Noise and total volatile organic compounds (TVOCs) levels at worksites were determined. We conducted hearing examinations to determine hearing thresholds. A worker was identified as having hearing loss if the mean threshold at 2000, 3000 and 4000 Hz in either ear was equal to or greater than 25 dB. Prevalence of occupational hearing loss was then evaluated. Using unconditional Logistic regression models, we estimated the odds ratios (ORs) of MSWL work associated with hearing loss.

Results

According to the job title for each worker, the study subjects were divided into 3 groups, including group 1 of 63 workers without MSWL occupational hazards exposure (control group), group 2 of 84 workers with a few or short-period MSWL occupational hazards exposure, and group 3 of 100 workers with continuous MSWL occupational hazards exposure. Both noise and TVOCs levels were significantly higher at worksites for group 3. Significantly poorer hearing thresholds at frequencies of 2000, 3000 and 4000 Hz were found in group 3, compared with that in group 1 and group 2. The overall prevalence rate of hearing loss was 23. 5%, with the highest in group 3 (36.0%). The OR of MSWL work associated with hearing loss was 3.39 (95% confidence interval [CI]: 1.28-8.96).

Conclusion

The results of this study suggest significantly higher prevalence of hearing loss among MSWL workers. Further studies are needed to explore possible exposure-response relationship between MSWL occupational hazards exposure and hearing loss.