Four buildings and a flush: Lessons from degraded water quality and recommendations on building water management.

A reduction in building occupancy can lead to stagnant water in plumbing, and the potential consequences for water quality have gained increasing attention. To investigate this, a study was conducted during the COVID-19 pandemic, focusing on water quality in four institutional buildings. Two of these buildings were old (>58 years) and large (>19,000 m2), while the other two were new (>13 years) and small (<11,000 m2). The study revealed significant decreases in water usage in the small buildings, whereas usage remained unchanged in the large buildings. Initial analysis found that residual chlorine was rarely detectable in cold/drinking water samples. Furthermore, the pH, dissolved oxygen, total organic carbon, and total cell count levels in the first draw of cold water samples were similar across all buildings. However, the ranges of heavy metal concentrations in large buildings were greater than observed in small buildings. Copper (Cu), lead (Pb), and manganese (Mn) sporadically exceeded drinking water limits at cold water fixtures, with maximum concentrations of 2.7 mg Cu L-1, 45.4 µg Pb L-1, 1.9 mg Mn L-1. Flushing the plumbing for 5 min resulted in detectable residual at fixtures in three buildings, but even after 125 min of flushing in largest and oldest building, no residual chlorine was detected at the fixture closest to the building's point of entry. During the pandemic, the building owner conducted fixture flushing, where one to a few fixtures were operated per visit in buildings with hundreds of fixtures and multiple floors. However, further research is needed to understand the fundamental processes that control faucet water quality from the service line to the faucet. In the absence of this knowledge, building owners should create and use as-built drawings to develop flushing plans and conduct periodic water testing.

Chemical characterization of microplastic particles formed in airborne waste discharged from sewer pipe repairs.

Microplastic particles are of increasing environmental concern due to the widespread uncontrolled degradation of various commercial products made of plastic and their associated waste disposal. Recently, common technology used to repair sewer pipes was reported as one of the emission sources of airborne microplastics in urban areas. This research presents results of the multi-modal comprehensive chemical characterization of the microplastic particles related to waste discharged in the pipe repair process and compares particle composition with the components of uncured resin and cured plastic composite used in the process. Analysis of these materials employs complementary use of surface-enhanced Raman spectroscopy, scanning transmission X-ray spectro-microscopy, single particle mass spectrometry, and direct analysis in real-time high-resolution mass spectrometry. It is shown that the composition of the relatively large (100 µm) microplastic particles resembles components of plastic material used in the process. In contrast, the composition of the smaller (micrometer and sub-micrometer) particles is significantly different, suggesting their formation from unintended polymerization of water-soluble components occurring in drying droplets of the air-discharged waste. In addition, resin material type influences the composition of released microplastic particles. Results are further discussed to guide the detection and advanced characterization of airborne microplastics in future field and laboratory studies pertaining to sewer pipe repair technology.

Diversity of organic components in airborne waste discharged from sewer pipe repairs.

Air-discharged waste from commonly used trenchless technologies of sewer pipe repairs is an emerging and poorly characterized source of urban pollution. This study reports on the molecular-level characterization of the atmospherically discharged aqueous-phase waste condensate samples collected at four field sites of the sewer pipe repairs. The molecular composition of organic species in these samples was investigated using reversed-phase liquid chromatography coupled with a photodiode array detector and a high-resolution mass spectrometer equipped with interchangeable atmospheric pressure photoionization and electrospray ionization sources. The waste condensate components comprise a complex mixture of organic species that can partition between gas-, aqueous-, and solid-phases when water evaporates from the air-discharged waste. Identified organic species have broad variability in molecular weight, molecular structures, and carbon oxidation state, which also varied between the waste samples. All condensates contained complex mixtures of oxidized organics, N- and S-containing organics, condensed aromatics, and their functionalized derivatives that are directly released to the atmospheric environment during installations. Furthermore, semi-volatile, low volatility, and extremely low volatility organic compounds comprise 75-85% of the total compounds identified in the waste condensates. Estimates of the component-specific viscosities suggest that upon evaporation of water waste material would form the semi-solid and solid phases. The low volatilities and high viscosities of chemical components in these waste condensates will contribute to the formation of atmospheric secondary organic aerosols and atmospheric solid nanoplastic particles. Lastly, selected components expected in the condensates were quantified and found to be present at high concentrations (1-20 mg L-1) that may exceed regulatory limits.

Residential Water Softeners Release Carbon, Consume Chlorine, and Require Remediation after Hydrocarbon Contamination.

Water quality impacts of new ion exchange point-of-entry residential softeners and their ability to be decontaminated following hydrocarbon exposure were investigated. During startup, significant amounts of total sulfur (445 ± 815 mg/L) and total organic carbon (937 ± 119 mg/L) were released into the drinking water that flowed through the softeners. Particulate organic carbon was released until the third regeneration cycle, and resin may also have been released. After one week of device use, softeners continued to cause organic carbon levels to be four to five times greater than background levels. Leached materials from the ion-exchange resin contributed to chlorine decay. When resins were exposed to hydrocarbon-contaminated water, they sorbed benzene, toluene, ethylbenzene, and xylenes (BTEX) and then desorbed the contaminants into drinking water during a 15 day flushing decontamination period. On day 15, benzene exceeded the federal drinking water limit for two of the four resins. The aged resin contributed to the greatest chlorine decay rates and sorbed and then retained the least amount of BTEX. Scale and biofilm on the aged resin likely prompted disinfectant reactivity and inhibited BTEX diffusion into the resin. Study results show that softeners exposed to hydrocarbon-contaminated water may need to be repeatedly flushed to remove BTEX contamination or be replaced. Additional work is recommended to better understand softener impacts on drinking water quality.

A Critical Review on the Factors that Influence Opportunistic Premise Plumbing Pathogens: From Building Entry to Fixtures in Residences.

Residential buildings provide unique conditions for opportunistic premise plumbing pathogen (OPPP) exposure via aerosolized water droplets produced by showerheads, faucets, and tubs. The objective of this review was to critically evaluate the existing literature that assessed the impact of potentially enhancing conditions to OPPP occurrence associated with residential plumbing and to point out knowledge gaps. Comprehensive studies on the topic were found to be lacking. Major knowledge gaps identified include the assessment of OPPP growth in the residential plumbing, from building entry to fixtures, and evaluation of the extent of the impact of typical residential plumbing design (e.g., trunk and branch and manifold), components (e.g., valves and fixtures), water heater types and temperature setting of operation, and common pipe materials (copper, PEX, and PVC/CPVC). In addition, impacts of the current plumbing code requirements on OPPP responses have not been assessed by any study and a lack of guidelines for OPPP risk management in residences was identified. Finally, the research required to expand knowledge on OPPP amplification in residences was discussed.

Pulmonary and neurological health effects associated with exposure to representative composite manufacturing emissions and corresponding alterations in circulating metabolite profiles.

Cured-in-place pipe (CIPP) technology is increasingly being utilized to repair aging and damaged pipes, however, there are concerns associated with the public health hazards of emissions. CIPP installation involves the manufacture of a new plastic composite pipe at the worksite and includes multiple variable components including resin material, curing methods, and operational conditions. We hypothesize styrene-based composite manufacturing emissions (CMEs) will induce greater pulmonary inflammatory responses and oxidative stress, as well as neurological toxicity compared with nonstyrene CMEs. Further, these CME-toxicological responses will be sex- and time-dependent. To test the hypothesis, representative CMEs were generated using a laboratory curing chamber and characterized using thermal desorption-gas chromatography-mass spectrometry and photoionization detector. Styrene was released during staying, isothermal curing, and cooling phases of the process and peaked during the cooling phase. Male and female C57BL6/J mice were utilized to examine alterations in pulmonary responses and neurotoxicity 1 day and 7 days following exposure to air (controls), nonstyrene-CMEs, or styrene-CMEs. Serum styrene metabolites were increased in mice exposed to styrene-CMEs. Metabolic and lipid profiling revealed alterations related to CIPP emissions that were resin-, time-, and sex-dependent. Exposure to styrene-CMEs resulted in an influx of lymphocytes in both sexes. Expression of inflammatory and oxidative stress markers, including Tnfα, Vcam1, Ccl2, Cxcl2, Il6, Cxcl1, Tgfß1, Tgmt2, and Hmox1, displayed alterations following exposure to emissions. These changes in pulmonary and neurological markers of toxicity were dependent on resin type, sex, and time. Overall, this study demonstrates resin-specific differences in representative CMEs and alterations in toxicity endpoints, which can potentially inform safer utilization of composite manufacturing processes.

Regulatory Significance of Plastic Manufacturing Air Pollution Discharged into Terrestrial Environments and Real-Time Sensing Challenges.

Cured-in-place-pipe (CIPP) is an onsite plastic manufacturing technology used in the U.S. and has not been evaluated for regulatory compliance with federal air pollution laws. The practice involves the discharge of manufacturing waste into the environment. The study goal was to estimate the magnitude of volatile organic compounds (VOCs) discharged into the atmosphere for styrene and nonstyrene composite manufacture and examine low-cost air monitoring sensor reliability. Time-resolved emission analysis revealed that VOC emission was not only isolated to the thermal curing period but also occurred before and after curing. In addition to the styrene monomer, other gas-phase hazardous air pollutants regulated under the Clean Air Act were also emitted. Based on typical CIPP installations, 0.9 to 16.6 U.S. tons of emitted VOCs were estimated for styrene CIPPs, and 0.09 to 1.6 U.S. tons of emitted VOCs were estimated for nonstyrene CIPPs. Because the number and size of CIPPs manufactured in a single community can vary, the total air pollution burden will significantly differ across communities. Low-cost VOC sensors commonly utilized near CIPP manufacturing activities did not accurately quantify styrene and should not be relied upon for that purpose. Up to several thousand-fold detection differences were observed. Regulatory evaluation of CIPP air pollution and PID sensor reliability assessments are recommended.

Atmospheric emission of nanoplastics from sewer pipe repairs.

Nanoplastic particles are inadequately characterized environmental pollutants that have adverse effects on aquatic and atmospheric systems, causing detrimental effects to human health through inhalation, ingestion and skin penetration1-3. At present, it is explicitly assumed that environmental nanoplastics (EnvNPs) are weathering fragments of microplastic or larger plastic debris that have been discharged into terrestrial and aquatic environments, while atmospheric EnvNPs are attributed solely to aerosolization by wind and other mechanical forces. However, the sources and emissions of unintended EnvNPs are poorly understood and are therefore largely unaccounted for in various risk assessments4. Here we show that large quantities of EnvNPs may be directly emitted into the atmosphere as steam-laden waste components discharged from a technology commonly used to repair sewer pipes in urban areas. A comprehensive chemical analysis of the discharged waste condensate has revealed the abundant presence of insoluble colloids, which after drying form solid organic particles with a composition and viscosity consistent with EnvNPs. We suggest that airborne emissions of EnvNPs from these globally used sewer repair practices may be prevalent in highly populated urban areas5, and may have important implications for air quality and toxicological levels that need to be mitigated.

School and childcare center drinking water: Copper chemistry, health effects, occurrence, and remediation.

The study goal was to better understand the risks of elevated copper levels at US schools and childcare centers. Copper health effects, chemistry, occurrence, and remediation actions were reviewed. Of the more than 98,000 schools and 500,000 childcare centers, only 0.2% had copper water testing data in the federal Safe Drinking Water Information System database. Of the facilities designated public water systems, about 13% had reported an exceedance. Schools that were not designated a public water system (PWS) also had exceedances. Few studies document levels in schools and childcare centers. Widely different sampling and remedial actions were reported. Flushing contaminated water was the most evaluated remedial action but was unreliable because copper quickly rebounded when flushing stopped. Building water treatment systems have been used, but some were not capable of making the water safe. The health risk was difficult to determine due to the limited occurrence data and lack of best management practice studies. A national drinking water testing campaign and field studies are recommended.

Prevalence of opportunistic pathogens in a school building plumbing during periods of low water use and a transition to normal use.

The spread of opportunistic pathogens via building water supply and plumbing is of public health concern. This study was conducted to better understand microbial water quality changes in a LEED-certified school building during low water use (Summer) and normal water use (Autumn). The copper plumbed building contained water saving devices, a hot water recirculation system, and received chloraminated drinking water from a public water system. Three separate sampling events were conducted during the summer break inside the building and another three sampling events were conducted after the school returned to session. Using quantitative PCR, Legionella spp. were detected in all water samples, followed by Mycobacterium spp. (99%). Mycobacterium avium (75%) and Acanthamoeba spp. (17.5%) throughout the building water system. Legionella pneumophila and Naegleria fowleri were not detected in any of the samples. The mean concentrations of Legionella spp., Mycobacterium spp., Mycobacterium avium, and Acanthamoeba spp. detected in water samples were 3.9, 5.7, 4.7, and 2.8 log10 gene copies per 100 ml, respectively. There was a statistically significantly difference in the mean concentrations of Legionella spp., Mycobacterium spp. and M. avium gene markers in water samples between school breaks and when school was in session. Cultivable Legionella were also detected in water samples collected during periods of low water use. This study highlights the need for routine proactive water quality testing in school buildings to determine the extent of drinking water quality problems associated with plumbing and direct action to remediate microbial colonization.

Bystander chemical exposures and injuries associated with nearby plastic sewer pipe manufacture: public health practice and lessons.

Cured-in-place pipes (CIPPs) are plastic liners manufactured inside existing damaged sanitary sewer, storm sewer, and water pipes that extend the service life of host pipes. This process often is conducted in neighborhoods and near roadways. Before, during, and after plastic manufacture, waste materials that include volatile materials are released into the air. Emissions from this manufacturing process can affect outdoor air quality and indoor air quality for buildings connected to the sewer system. We identified key issues and solicited stakeholder feedback to estimate and manage public health risks of CIPP-generated chemical air pollution. A work group representing 13 U.S. agencies and public health associations provided feedback and prioritized public health issues for action. To mitigate potential public and occupational health risks, additional testing and public health educational efforts were recommended. An improved understanding of CIPP chemical exposure pathways, as well as stakeholder needs and interests, is essential.

Emergency responder and public health considerations for plastic sewer lining chemical waste exposures in indoor environments.

The cured-in-place pipe (CIPP) manufacturing process is used to repair buried pipes, and its waste commonly discharged into the air can enter nearby buildings. Exposure can prompt illness and the need for medical care. A mass balance model was applied to estimate indoor styrene concentrations due to intrusion of CIPP emissions through plumbing under different bathroom ventilation conditions. To better understand building contamination and recommend emergency response actions, calculations to estimate chemical intrusion through plumbing were developed. Field reports and study calculations showed that contractor-applied external pressures during plastic manufacture have and can displace plumbing trap water seals. Modeled styrene vapor concentrations that entered the building (1, 300, 1000 ppm) were similar to those measured at CIPP worksites. Modeling revealed that in some cases, bathroom exhaust fan operation during a CIPP project may increase indoor styrene concentrations due to enhanced entrainment of styrene-laden air from the sink and toilet. However, styrene concentrations decreased with increasing air leakage across the bathroom door due to reduced suction from the plumbing system. CIPP waste discharge should be treated as a hazardous material release and can pose a threat to human health. Immediate building evacuation, respiratory protection, provision of medical assistance, source elimination, and building decontamination are recommended.

Considerations for large building water quality after extended stagnation.

The unprecedented number of building closures related to the coronavirus disease (COVID-19) pandemic is concerning because water stagnation will occur in many buildings that do not have water management plans in place. Stagnant water can have chemical and microbiological contaminants that pose potential health risks to occupants. Health officials, building owners, utilities, and other entities are rapidly developing guidance to address this issue, but the scope, applicability, and details included in the guidance vary widely. To provide a primer of large building water system preventative and remedial strategies, peer-reviewed, government, industry, and nonprofit literature relevant to water stagnation and decontamination practices for plumbing was synthesized. Preventative practices to help avoid the need for recommissioning (e.g., routine flushing) and specific actions, challenges, and limitations associated with recommissioning were identified and characterized. Considerations for worker and occupant safety were also indicated. The intended audience of this work includes organizations developing guidance.

Impacts of Municipal Water-Rainwater Source Transitions on Microbial and Chemical Water Quality Dynamics at the Tap.

When rainwater harvesting is utilized as an alternative water resource in buildings, a combination of municipal water and rainwater is typically required to meet water demands. Altering source water chemistry can disrupt pipe scale and biofilm and negatively impact water quality at the distribution level. Still, it is unknown if similar reactions occur within building plumbing following a transition in source water quality. The goal of this study was to investigate changes in water chemistry and microbiology at a green building following a transition between municipal water and rainwater. We monitored water chemistry (metals, alkalinity, and disinfectant byproducts) and microbiology (total cell counts, plate counts, and opportunistic pathogen gene markers) throughout two source water transitions. Several constituents including alkalinity and disinfectant byproducts served as indicators of municipal water remaining in the system since the rainwater source does not contain these constituents. In the treated rainwater, microbial proliferation and Legionella spp. gene copy numbers were often three logs higher than those in municipal water. Because of differences in source water chemistry, rainwater and municipal water uniquely interacted with building plumbing and generated distinctively different drinking water chemical and microbial quality profiles.

An emerging mobile air pollution source: outdoor plastic liner manufacturing sites discharge VOCs into urban and rural areas.

The in situ manufacture of cured-in-place-pipe (CIPP) plastic liners in damaged sewer pipes is an emerging mobile source of anthropogenic air pollution. Evidence indicates volatile organic compounds (VOCs) can be released before, during, and after manufacture. The chemical composition of a popular uncured styrene-based CIPP resin was examined, along with the VOCs that remained in the new cured composite. The roles of curing temperature and heating time in waste discharged into the air were examined. Uncured resin contained approximately 39 wt% VOCs. Multiple hazardous air pollutants were present, however, 61 wt% of the uncured resin was not chemically identified. A substantial mass of VOCs (8.87 wt%) was emitted into the air during manufacture, and all cured composites contained about 3 wt% VOCs. Some VOCs were created during manufacture. Curing temperature (65.5-93.3 °C) and heating time (25-100 min) did not cause different composite VOC loadings. High styrene air concentrations inhibited the detection of other VOCs in air. It is estimated that tens of tons of VOCs may be emitted at a single CIPP manufacturing site. Regulators should consider monitoring, and potentially regulating, these growing mobile air pollution and volatile chemical product sources as they are operating in urban and rural areas often in close proximity to residential and commercial buildings.

Competitive heavy metal adsorption onto new and aged polyethylene under various drinking water conditions.

The study goal was to identify factors that influence copper (Cu), iron (Fe), lead (Pb), manganese (Mn), and zinc (Zn) loading on new and aged low-density polyethylene (LDPE) under various drinking water conditions. The applied aging procedure increased LDPE surface area, hydrophilicity and the number of oxygen containing functional groups. Aged LDPE adsorbed up to a 5 fold greater metals than the new LDPE: Cu > Pb, Zn > Mn. Water pH (5.5 to 10.5) significantly altered LDPE surface metal loading. The organic carbon leached from plastic pipes inhibited Cu adsorption (-43.8%), but other metals were less impacted (-5.7% to -9.1%). The addition of free chlorine and corrosion inhibitor retarded metal adsorption to suspended LDPE materials. Overall, by changing water conditions total metal loadings (i.e., Cu, Mn, Pb and Zn) were altered 20.1 to 35.4%. When Fe was present, Cu (-4.0%) and Pb (-4.5%) loadings were reduced, while lesser impacts were found for Mn and Zn. Cu2+, Pb2+ and Zn2+ hydroxides and oxides were identified as the major metal deposit forms on the LDPE surface by XPS. To better predict metal fate in plastic piping systems, plastic surface characteristics, dissolved organics, water pH, hydraulic conditions and microbial growth should be considered.

Corrosion of upstream metal plumbing components impact downstream PEX pipe surface deposits and degradation.

Plastic pipes have been and are being installed downstream of metal drinking water plumbing components. Prior research has suggested that such pipe configurations may induce plastic pipe degradation and even system failure. To explore the impact of upstream metal plumbing components on downstream plastic pipes, field- and bench-scale experiments were conducted. Six month old galvanized iron pipes (GIPs) and downstream crosslinked polyethylene (PEX) pipes were exhumed from a residential home. Calcium, iron, manganese, phosphorous, and zinc were the most abundant elements on both GIPs and PEX pipes. Black and yellow deposits were found on some of the exhumed PEX pipe inner walls, which were mainly copper, iron, and manganese oxides (CuO, Cu(OH)2, Fe2O3, FeOOH and MnO2). Follow-up bench-scale experiments revealed that metal levels in the drinking water did not always predict metal loadings on plastic pipe surfaces. The pH 4 water resulted in a greater amount of metals released into the bulk water, but the pH 7.5 water resulted in a greater amount of metals deposited on the PEX pipe surfaces. Hot water (55 °C) induced a greater amount of organics released and higher metal loadings on PEX pipe surfaces at pH 7.5. ATR-FTIR analysis showed that at 55 °C, PEX pipes connected to copper and brass components had the greatest oxidation functional group peak intensity (COOC, CO, and COC). This study highlights potential downstream plastic pipe degradation and metal deposition, which may cause plumbing problems and failures for building owners, inhabitants, and water utilities.

In vitro toxicity assessment of emitted materials collected during the manufacture of water pipe plastic linings.

Objectives: US water infrastructure is in need of widespread repair due to age-related deterioration. Currently, the cured-in-place (CIPP) procedure is the most common method for water pipe repair. This method involves the on-site manufacture of a new polymer composite plastic liner within the damaged pipe. The CIPP process can release materials resulting in occupational and public health concerns. To understand hazards associated with CIPP-related emission exposures, an in vitro toxicity assessment was performed. Materials and Methods: Mouse alveolar epithelial and alveolar macrophage cell lines and condensates collected at 3 worksites utilizing styrene-based resins were utilized for evaluations. All condensate samples were normalized based on the major emission component, styrene. Further, a styrene-only exposure group was used as a control to determine mixture related toxicity. Results: Cytotoxicity differences were observed between worksite samples, with the CIPP worksite 4 sample inducing the most cell death. A proteomic evaluation was performed, which demonstrated styrene-, worksite-, and cell-specific alterations. This examination of protein expression changes determined potential biomarkers of exposure including transglutaminase 2, advillin, collagen type 1, perilipin-2, and others. Pathway analysis of exposure-induced proteomic alterations identified MYC and p53 to be regulators of cellular responses. Protein changes were also related to pathways involved in cell damage, immune response, and cancer. Conclusions: Together these findings demonstrate potential risks associated with the CIPP procedure as well as variations between worksites regarding emissions and toxicity. Our evaluation identified biological pathways that require a future evaluation and also demonstrates that exposure assessment of CIPP worksites should examine multiple chemical components beyond styrene, as many cellular responses were styrene-independent.

Analysis of building plumbing system flushing practices and communications.

Drinking water distribution system contamination incidents can prompt public agencies and drinking water utilities to issue do-not-drink and do-not-use advisories. After the contaminant is cleared from distribution mains, consumers are often directed to flush their plumbing. However, little validated guidance and few evaluated communications strategies are available on using flushing to decontaminate building water systems. Additionally, limited data support the effectiveness of current practices and recommendations. In this study, expert elicitation was used to assess existing flushing guidance and develop validated flushing guidance and communications for single-family residences. The resulting guidance recommends progressively opening all cold-water taps from the closest to point of entry to the furthest and allowing the water to run for at least 20 minutes. Hot-water taps should be opened progressively and run for at least 75 minutes. The guidance language and format conformed to grade-level and readability scores within recommended health communication ranges. The readability of eight other flushing guidance documents was also evaluated for contamination incidents from 2008-2015. Seven were written at a 10th-12th grade level, above the 6th-7th grade level recommended for health communications.

Considerations for emission monitoring and liner analysis of thermally manufactured sewer cured-in-place-pipes (CIPP).

Cured-in-place-pipes (CIPP) are plastic liners chemically manufactured inside existing damaged sewer pipes. They are gaining popularity in North America, Africa, Asia, Europe, and Oceania. Volatile and semi-volatile organic compound (VOC/SVOC) emissions from storm sewer CIPP installations were investigated at a dedicated outdoor research site. Tedlar bag, sorbent tube, and photoionization detector (PID) air sampling was conducted for five steam-CIPP installations and was coupled with composite characterizations. New CIPPs contained up to 2.21 wt% volatile material and only 6-31% chemical mass extracted per CIPP was identified. Each 6.1 m [20 ft] liner contained an estimated 5-10 kg [11-22 lbs] of residual chemical. Extracted chemicals included hazardous air pollutants and suspected and known carcinogens that were not reported by others. These included monomers, monomer oxidation products, antioxidants, initiator degradation products, and a plasticizer. PID signals did not accurately represent styrene air concentration differing sometimes by 10s- to 1000s-fold. Multiple VOCs found in air samples likely affected PID responses. Styrene (>86.4 ppmv) and methylene chloride (>1.56 ppmv) air concentrations were likely greater onsite and phenol was also detected. Additional studies are needed to examine pollutant emissions so process monitoring can be improved, and environment impacts and associated human exposures can be minimized.