Nitrogen dioxide and ozone as factors in the availability of lead from lead-based paints

Seasonal disparities in airborne lead (Pb) and associated foliar uptake by ryegrass (Lolium perenne L.): A Pb isotopic approach

Foliar uptake of airborne lead (Pb) may be particularly important for Pb accumulation in plant organs. However, the aerosol bioconcentration factor (BCF) in different seasons has seldom been reported. In the present study, we collected ryegrass (Lolium perenne L.) and size-segregated aerosols (SSA) during the corresponding growing seasons, and analyzed these for both Pb concentrations and isotopic ratios. Airborne Pb showed a seasonally varying concentration that was approximately 20% higher in winter than in spring. The bioavailability index, however, was higher in spring. Coupling the stable isotope technique with the bioavailable Pb of aerosol was more reliable in identifying airborne Pb accumulation in leaves than the total determination, suggesting that the hydrophilic absorption pathway was probably dominant for the foliar uptake of Pb in ryegrass. Contributions of airborne Pb accumulation were 88%-92% for washed ryegrass growing outdoors, indicating that the foliar uptake of Pb in the field was mainly from atmospheric deposition. The aerosol BCF of Pb for ryegrass was 6.4-11.4 m³/g in winter and 22.9-31.5 m³/g in spring. The increased aerosol BCF in spring was due to the suitable temperature, abundant rainfall, and increased Pb solubility of the aerosol. Therefore, our results indicate that, for the foliar uptake of Pb, both the aerosol Pb concentration, composition, and seasonal influence should be considered.

Lead-based paint remains a major public health concern: A critical review of global production, trade, use, exposure, health risk, and implications

Human exposure to lead (Pb) is a growing global public health concern. Elevated blood lead is thought to cause the mental retardation of >0.6 million children globally each year, and has recently been attributed to ~18% of all-cause mortality in the US. Due to the severe health risk, the international community, led by the United Nations Environment Programme (UNEP) and the World Health Organization (WHO), is actively supporting the global phase-out of lead-based paint by 2020. However, there are many significant hurdles on the way to achieving this goal. In light of the importance of the lead-based paint issue, and the urgency of achieving the 2020 phase-out goal, this review provides critical insights from the existing scientific literature on lead-based paint, and offers a comprehensive perspective on the overall issue. The global production and international trade of lead-based paints across Asia, Africa, Latin America, and Europe are critically discussed - revealing that lead-based paints are still widely used in many low and middle-income developing countries, and that the production and trade of lead-based paint is still wide-spread globally. In India, as well as many south-east Asian, African, Latin American and European countries, lead concentrations in paints often exceed 10,000 mg/kg. This will certainly pose a serious global threat to public health from surfaces painted with these products for many decades to come. The sources and pathways of exposure are further described to shed light on the associated health risk and socioeconomic costs. Finally, the review offers an overview of the potential intervention and abatement strategies for lead-based paints. In particular, it was found that there is a general lack of consensus on the definition of lead based paint; and, strengthening regulatory oversight, public awareness, and industry acceptance are vital in combating the global issue of lead based paint.

Relative bioaccessibility of Pb-based paint in soil

The threat posed by lead (Pb) in soil for pediatric populations continues to be a public health issue. In long-established residential areas, a principal source of Pb in soil is likely to be old Pb-based paint originating from building surfaces. The health hazard posed by Pb from paint in soil will likely depend on quantity of paint incorporated, its Pb-mineral composition, whether the Pb is locked in some other material and the paint residence time in the soil (degree of aging). Here the relative bioavailability (RBA) of Pb in different types of Pb-bearing paint has been assessed. Tests were performed with individual paints, with paints mixed with a low-Pb soil, and with paints mixed with soil and the biogenic phosphate apatite II. Thirteen Pb-bearing paint samples were ground and passed through 250- and 100-µm screens. Samples nominally <100 µm from all the paints were analyzed, and six of the paints for which there was sufficient material in the 100- to 250-µm-size range were also tested. RBA extraction of Pb employed a simulated gastric fluid (SGF) of HCl and glycine adjusted to a pH of 1.5 in which samples were agitated (in an end-over-end rotator) for 2 h. Original paints were examined by SEM/EDX, and by XRD, residues collected after RBA extraction were examined by SEM/EDX. The concentration of Pb in the extraction fluid was measured by AAS. The quantity of Pb mobilized in each test batch was approximately an order of magnitude less in the paint-soil mix compared to the corresponding paint-only sample. The difference in the amount of Pb extracted from the paint-soil mix compared to the paint-soil-phosphate mix was minimal. However, in the post-RBA residues of the paint-soil mix, a PbCl precipitate was observed, and in the extraction residues of the paint-soil-apatite II mixes PbClP phases were recorded. Precipitation of these secondary phases obviously modified the amount of Pb in the extraction fluid, and this may need to be considered, i.e., under-reporting of extractable Pb, when this form of in vitro extraction is used to determine the RBA of Pb in environmental media.

ATR-IR study of ozone initiated heterogeneous oxidation of squalene in an indoor environment

There has been a surge of interest in interfacial ozone chemistry for its application in indoor air quality and public health. Squalene, one of the most abundant ozone reactive constituents in an indoor environment, has received increasing attention lately, and a number of studies have been devoted to its heterogeneous interaction with ozone in actual and simulated settings. At present, there is still a large discrepancy in the measurement of the reactive uptake coefficient of ozone onto a squalene surface, and knowledge about this system remains incomplete. In this work, we investigated the ozone initiated heterogeneous oxidation of squalene using attenuated total reflection infrared spectroscopy (ATR-IR). We measured pseudo-first-order rate constants and uptake coefficients based on time dependent absorbance changes in C═C (1668 cm(-1)) and C═O (1730 cm(-1)) vibration bands. The uptake coefficients are (1.7 ± 0.2) × 10(-4) from the C═C band and (5.1 ± 0.7) × 10(-4) from the C═O band. The latter is likely an upper limit of reaction probability for ozone uptake onto squalene. Studies of temperature (5-32 °C) and relative humidity (0 and 80% RH) dependence revealed that indoor temperatures and RHs did not affect reaction kinetics. The insignificant RH effect is probably due to the weak interaction between water and squalene molecules. We quantitatively characterized the hydrophilicity and redox activity of squalene before and after exposure to ozone for the first time, and observed considerable enhancements in both hydrophilicity and redox activity during reaction. This may imply that ozone initiated heterogeneous oxidation could pose a higher public health risk in an indoor environment, and it may help explain some of the adverse health effects associated with elevated indoor pollutants.

Heterogeneous atmospheric chemistry of lead oxide particles with nitrogen dioxide increases lead solubility: environmental and health implications

Heterogeneous chemistry of nitrogen dioxide with lead-containing particles is investigated to better understand lead metal mobilization in the environment. In particular, PbO particles, a model lead-containing compound due to its widespread presence as a component of lead paint and as naturally occurring minerals, massicot, and litharge, are exposed to nitrogen dioxide at different relative humidity. X-ray photoelectron spectroscopy (XPS) shows that upon exposure to nitrogen dioxide the surface of PbO particles reacts to form adsorbed nitrates and lead nitrate thin films with the extent of nitrate formation relative humidity dependent. NO(2)-exposed PbO particles are found to have an increase in the amount of lead that dissolves in aqueous suspensions at circumneutral pH compared to particles not exposed. These results point to the potential importance and impact that heterogeneous chemistry with trace atmospheric gases can have on increasing solubility and therefore the mobilization of heavy metals, such as lead, in the environment. This study also shows that surface intermediates that form, such as adsorbed lead nitrates, can yield higher concentrations of lead in water systems. These water systems can include drinking water, groundwater, estuaries, and lakes.

Measuring the penetration of ambient ozone into residential buildings

Much of human exposure to ambient ozone and ozone reaction byproducts occurs inside buildings. However, there are currently no experimental data on the ability of ozone to penetrate through building envelopes and into residences. This paper presents a method to determine the penetration factor for ozone in buildings, and applies it in an unoccupied test house and seven single-family residences. The mean (±SD) ozone penetration factor was measured as 0.79 ± 0.13 in the eight homes using this method, ranging from 0.62 ± 0.09 to 1.02 ± 0.15. An analysis of tests across the homes revealed that ozone penetration was significantly higher in homes with more painted wood envelope materials, homes with larger air leakage exponents from fan pressurization tests, and older homes. The test method utilizes a large calibrated fan to elevate air exchange rates and steady-state indoor ozone concentrations to levels that can be accurately measured, so there is a potential for overpredicting ozone penetration factors. However, evidence suggests that this bias is likely small in most of the homes, and, even if a bias exists, the measured ozone penetration factors were lower than the usual assumption of unity in seven of the eight tested homes.

Chemistry in indoor environments: 20 years of research

In the two decades since the first issue of Indoor Air, there have been over 250 peer-reviewed publications addressing chemical reactions among indoor pollutants. The present review has assembled and categorized these publications. It begins with a brief account of the state of our knowledge in 1991 regarding 'indoor chemistry', much of which came from corrosion and art conservation studies. It then outlines what we have learned in the period between 1991 and 2010 in the context of the major reference categories: gas-phase chemistry, surface chemistry, health effects and reviews/workshops. The indoor reactions that have received the greatest attention are those involving ozone-with terpenoids in the gas-phase as well as with the surfaces of common materials, furnishings, and the occupants themselves. It has become clear that surface reactions often have a larger impact on indoor settings than do gas-phase processes. This review concludes with a subjective list of major research needs going forward, including more information on the decomposition of common indoor pollutants, better understanding of how sorbed water influences surface reactions, and further identification of short-lived products of indoor chemistry. Arguably, the greatest need is for increased knowledge regarding the impact that indoor chemistry has on the health and comfort of building occupants.

PRACTICAL IMPLICATIONS

Indoor chemistry changes the type and concentration of chemicals present in indoor environments. In the past, products of indoor chemistry were often overlooked, reflecting a focus on stable, relatively non-polar organic compounds coupled with the use of sampling and analytical methods that were unable to 'see' many of the products of such chemistry. Today, researchers who study indoor environments are more aware of the potential for chemistry to occur. Awareness is valuable, because it leads to the use of sampling methods and analytical tools that can detect changes in indoor environments resulting from chemical processes. This, in turn, leads to a more complete understanding of occupants' chemical exposures, potential links between these exposures and adverse health effects and, finally, steps that might be taken to mitigate these adverse effects.