The behavior and routes of lead exposure in pregrasping infants

Positive outcomes from U.S. lead regulations, continued challenges, and lessons learned for regulating emerging contaminants

Albeit slow and not without its challenges, lead (Pb) emissions and sources in the United States (U.S.) have decreased immensely over the past several decades. Despite the prevalence of childhood Pb poisoning throughout the twentieth century, most U.S. children born in the last two decades are significantly better off than their predecessors in regard to Pb exposure. However, this is not equal across demographic groups and challenges remain. Modern atmospheric emissions of Pb in the U.S. are nearly negligible since the banning of leaded gasoline in vehicles and regulatory controls on Pb smelting plants and refineries. This is evident in the rapid decrease of atmospheric Pb concentrations across the U.S. over the last four decades. One of the most significant remaining contributors to air Pb is aviation gasoline (avgas), which is minor compared to former Pb emissions. However, continual exposure risks to Pb exist in older homes and urban centers, where leaded paint and/or historically contaminated soils + dusts can still harm children. Thus, while effective in eliminating nearly all primary sources of Pb in the environment, the slow rate of U.S. Pb regulation has led to legacy sources of Pb in the environment. More proactive planning, communication, and research of commonly used emerging contaminants of concern that can persist in the environment long after their initial use (i.e., PFAS) should be prioritized so that the same mistakes are not made again.

Demonstrational gardens with EDTA-washed soil. Part I: Remediation efficiency, effect on soil properties and toxicity hazards

The viable chelator-based soil washing has yet to be demonstrated on a larger scale. Soil containing 1850, 3830 and 21 mg kg^-1 Pb, Zn and Cd, respectively, was washed with 100 mmol EDTA kg^-1 in a series of 16 batches (1 ton soil/batch) using the new ReSoil® technology. The ReSoil® recycled the process water and 85% of the EDTA, producing no wastewater and 14.4 kg ton^-1 of waste. The soil washing removed 71, 28 and 53% of Pb, Zn and Cd, respectively, mainly from the carbonate fraction, saturated the soil with basic cations and increased the soil pH by up to 0.5 units. Raised beds (4 × 1 × 0.5 m) with original (contaminated) and remediated soil were constructed as lysmeters, and local produce was grown from July 2018 to November 2019. Throughout the gardening period, the concentration of Pb and Cd in the leachates from the remediated soil was lower and that of Zn was higher than in the original soil. Remediation decreased the concentration of plant-available and mobile toxic metals, as determined by CaCl₂ and NH₄NO₃ extractions, and reduced the bioavailability of Pb, Zn, and Cd in the simulated human gastrointestinal phase by an average of 4.3, 1.7 and 2.7-fold, respectively. Revitalization with vermicompost, earthworms and rhizosphere soil, and spring fertilisation with compost and manure, had no significant effect on the mobility and accessibility of the toxic metals. The ReSoil® is a cost-effective technology (material cost = 18.27 € ton^-1 soil) and showed the prospect of sustainable reuse of remediated soil.

Soil washing with biodegradable chelating agents and EDTA: Technological feasibility, remediation efficiency and environmental sustainability

In washing soils contaminated with toxic metals, the replacement of recalcitrant EDTA with biodegradable chelators has gained high expectations. Herein we investigated the feasibility of using EDTA and biodegradable GLDA, EDDS and IDS under conditions pertinent to operational remediation technology, in a pilot-scale experiment. GLDA and IDS did not precipitate from process solutions, which lessened their recyclability. In other process parameters, chelator supplement, Na-saturation of process solutions and processing time, EDTA outperformed biodegradable chelators. Treatment with EDTA was also the most effective in total Pb and Zn removal and least impacted soil properties. GLDA was slightly better in Cd removal. EDDS and IDS were inefficient. All chelators effectively removed easily-available Pb, Zn and Cd from the exchangeable soil fraction. EDTA was the most efficient chelator in reducing the bioaccessibility of Pb and GLDA in reducing the bioaccessibility of Cd from simulated human gastrointestinal tract. Treatment with GLDA had an edge in reducing plant bioaccessibility of toxic metals, but induced worrying leachability of Pb. This was 8.3-times higher than with the process with EDTA and 3.4-times higher than in original soil. In general, our results demonstrate the advantage of EDTA over tested biodegradable chelators in process and remediation efficiency and environmental safety.

The association between prenatal endocrine-disrupting chemical exposure and altered resting-state brain fMRI in teenagers

Many studies have reported that prenatal exposure to endocrine-disrupting chemicals (EDCs) can cause adverse behavioral effects or cognitive dysfunction in children. This study aimed to investigate a relationship of the concentration of prenatal EDCs and brain function in teenagers. We recruited 59 mother-child pairs during the third trimester of pregnancy, and collected and examined the concentration of EDCs, such as heavy metals, phthalates and perfluoroalkyl substances (PFASs), in maternal urine and serum. Resting-state functional magnetic resonance imaging (rs-fMRI) data were collected in teenagers 13-16 years of age, and fractional amplitude of low-frequency fluctuation (fALFF) and regional homogeneity (ReHo) were performed to find the association between maternal EDC concentrations and the functional development of the teenage brain. We found a correlation between MBP concentration and activity in the superior frontal gyrus, middle frontal gyrus, middle temporal gyrus and inferior temporal gyrus in the combined group of boys and girls. We also observed a correlation between MBzP concentration and activity in the anterior cingulum gyrus and insula in girls. We found a correlation between lead concentration and activity in the cuneus in the combined group. We also observed a correlation between MeHg concentration and activity in the superior temporal gyrus, caudate nucleus and putamen in the combined group. The PFOS results revealed a negative relationship between activity in the right putamen in boys, girls and the combined group after phthalate or heavy metals were applied as covariates. The PFNA results showed a negative correlation between activity in the left/right putamen and left caudate nucleus in boys, girls and the combined group after phthalate, heavy metals or PFOS were applied as covariates. We examined the correlations between maternal EDC concentrations and brain development and found that the associations with resting-state teenage brains in some circumstances are sex-related.

Environmental arsenic, cadmium and lead dust emissions from metal mine operations: Implications for environmental management, monitoring and human health

Although blood lead values in children are predominantly falling globally, there are locations where lead exposure remains a persistent problem. One such location is Broken Hill, Australia, where the percentage of blood lead values >10 μg/dL in children aged 1-4 years has risen from 12.6% (2010), to 13% (2011) to 21% (2012). The purpose of this study was to determine the extent of metal contamination in places accessible to children. This study examines contemporary exposure risks from arsenic, cadmium, lead, silver and zinc in surface soil and dust, and in pre- and post-play hand wipes at six playgrounds across Broken Hill over a 5-day period in September 2013. Soil lead (mean 2,450 mg/kg) and zinc (mean 3,710 mg/kg) were the most elevated metals in playgrounds. Surface dust lead concentrations were consistently elevated (mean 27,500 μg/m(2)) with the highest lead in surface dust (59,900 μg/m(2)) and post-play hand wipes (60,900 μg/m(2)) recorded close to existing mining operations. Surface and post-play hand wipe dust values exceeded national guidelines for lead and international benchmarks for arsenic, cadmium and lead. Lead isotopic compositions ((206)Pb/(207)Pb, (208)Pb/(207)Pb) of surface dust wipes from the playgrounds revealed the source of lead contamination to be indistinct from the local Broken Hill ore body. The data suggest frequent, cumulative and ongoing mine-derived dust metal contamination poses a serious risk of harm to children.

Follow-up study on lead exposure in children living in a smelter community in northern Mexico

BACKGROUND

To study the changes of children lead exposure in the city of Torreon during the last five years, after environmental and public health interventions, using the timeline of lead in blood concentration as the biomarker of exposure and its relation to lead in soil concentrations.

METHODS

This follow-up study started in 2001 and consisted of 232 children living in nine neighborhoods in Torreon. Children were tested at 0, 6, 12 and 60 months. Lead in blood concentrations, Hemoglobin, Zinc-Protoporphyrin, anthropometric measures and socioeconomic status questionnaire was supplied to the parents.

RESULTS

Median and range of lead in blood concentrations obtained at 0, 6, 12, 60 months were: 10.12 μg/dl (1.9 - 43.8), 8.75 μg/dl (1.85 - 41.45), 8.4 μg/dl (1.7 - 35.8) and 4.4 μg/dl (1.3 - 30.3), respectively. The decrease of lead in blood levels was significantly related to ages 0, 6, 12 and 60 months of the follow-up study. The timeline of B-Pb was associated with the timeline of lead in soil concentrations.

CONCLUSIONS

B-Pb levels have significantly decreased in the group of children studied. This could be explained by a) environmental interventions by authorities and the smelter companies, b) normal changes in hygienic habits as children age and c) lead redistribution from blood to hard tissues.

Living in a sea of lead--changes in blood- and hand-lead of infants living near a smelter

Thirteen infants born into the lead contaminated environment of Port Pirie, South Australia, were followed approximately monthly from birth until they were about 36 months. Blood-lead levels of infants at birth were similar to their mothers but fell rapidly during the first 35 days of life. Thereafter, infants born with blood-lead levels at about 2-4 microg/dl began a slow linear increase until 14-18 months where a plateau occurred of 10.8-17.2 microg/dl. The blood-lead levels were well correlated with hand-lead loadings of infant (r(2)=0.72, P<0.01, log transformed data) and mother (r(2)=0.62, P<0.01, log transformed data) unless the birth lead level was exceptionally high. The principle factor determining exposure was the impact of smelter emissions on the house. Blood-lead increase was caused by the relatively more rapid increase in dose of lead compared with the increasing body mass, which was related directly to the maturation of motor development. Hand-lead of mothers were closely related to both infants' blood- and hand-lead levels until the point of blood-lead plateau then substantially fell as infants began to walk unaided. The estimated slope factor using the ICRP model was 0.75-0.94 microg/dl per microg/day with a maximum daily dose of 3-5 microg/kg/day, assuming 45% absorption. Ingestion appears to be the most likely route for at least 95% of the dose.

How important is inadvertent ingestion of hazardous substances at work?

Much is known about human exposure to workplace hazardous substances by inhalation and from skin contact, but there has been little systematic research into ingestion of hazardous substances used at work. This review attempts to identify whether inadvertent ingestion of hazardous substances is an important route of exposure in the workplace and examines possible methods that could be used to quantify ingestion exposure. A number of papers highlight jobs and substances where inadvertent ingestion may be important, typically through case reports or from a theoretical analysis. These scenarios involve exposure to some metals or metal compounds, pharmaceuticals, pesticides, some infectious agents, unsealed radioactive sources and some high molecular weight allergens. In total we estimate that about 4.5 million workers in the UK could have some regular non-trivial intake of hazardous substances by inadvertent ingestion. A conceptual analysis of inadvertent ingestion exposure highlights the role of hand-to-mouth and object-to-mouth events as the primary exposure processes. Two exposure 'compartments' are defined: the peri-oral area (i.e. the area of skin around the outside of the mouth) and the oral cavity. Several options are highlighted for exposure-related measurements, including peri-oral wipes, saliva samples, mouth-rinse samples, hand-wipes and under-nail scrapings. Further research is necessary to define which measurements may be most informative. Human behaviour has a key role in determining inadvertent ingestion exposure. For example, some people are habitual nail biters or repeatedly touch their mouth, both of which will increase the chance of ingesting contaminants on their hands. The frequency that people touch their face is dependant on the circumstances of their work and probably the degree of psychological stress they are under. A proper understanding of the importance of these factors will help in designing interventions to reduce the risks from ingesting hazardous substances at work. When making inhalation or dermal exposure measurements we recommend that details of personal behaviours should be recorded so that some estimate of ingestion risks can be inferred. It is possible that inadvertent ingestion of hazardous substances at work may become more important as employers put more emphasis on controlling inhalation and dermal exposures. Further research is necessary to ensure that risk reduction strategies for inadvertent ingestion of hazardous substances are appropriate and effective.

Video methods in the quantification of children's exposures

In 1994, Stanford University's Exposure Research Group (ERG) conducted its first pilot study to collect micro-level activity time series (MLATS) data for young children. The pilot study involved videotaping four children of farm workers in the Salinas Valley of California and converting their videotaped activities to valuable text files of contact behavior using video-translation techniques. These MLATS are especially useful for describing intermittent dermal (i.e., second-by-second account of surfaces and objects contacted) and non-dietary ingestion (second-by-second account of objects or hands placed in the mouth) contact behavior. Second-by-second records of children contact behavior are amenable to quantitative and statistical analysis and allow for more accurate model estimates of human exposure and dose to environmental contaminants. Activity patterns data for modeling inhalation exposure (i.e., accounts of microenvironments visited) can also be extracted from the MLATS data. Since the pilot study, ERG has collected an immense MLATS data set for 92 children using more developed and refined videotaping and video-translation methodologies. This paper describes all aspects required for the collection of MLATS including: subject recruitment techniques, videotaping and video-translation processes, and potential data analysis. This paper also describes the quality assurance steps employed for these new MLATS projects, including: training, data management, and the application of interobserver and intraobserver agreement during video translation. The discussion of these issues and ERG's experiences in dealing with them can assist other groups in the conduct of research that employs these more quantitative techniques.