Comparative life cycle assessment of copper and gold recovery from waste printed circuit boards: Pyrometallurgy, chemical leaching and bioleaching

Printed circuit boards (PCBs) make up a substantial amount of electronic waste (e-waste) generated annually. Waste PCBs contain high quantities of copper and gold in comparison to natural ores. As such, "urban mining" of waste PCBs to recover these metals is of commercial interest. In this work, we used life cycle assessment to compare the environmental impact of four copper and gold recovery processes. We evaluated pyrometallurgy, chemical leaching, and bioleaching, as well as a hybrid leaching process that uses bioleaching to recover copper and chemical leaching to recover gold. Furthermore, we considered differences in environmental impact based on differences in electricity sources. If electricity comes from fossil fuels, the pyrometallurgical process results in the lowest environmental impact in all impact categories studied. If electricity comes from carbon-free sources, the pyrometallurgical process results in the lowest environmental impact in all categories studied except global warming, where the hybrid leaching process results in the lowest impact. In all cases, metal recovery from waste PCBs leads to lower environmental impact than primary metal production. Our goal is to guide e-waste recyclers towards more environmentally sustainable metal recovery processes and to provide knowledge gaps in the field to guide future research.

Advancing chemical hazard assessment with decision analysis: A case study on lithium-ion and redox flow batteries used for energy storage

Batteries are important for promoting renewable energy, but, like most engineered products, they contain multiple hazardous materials. The purpose of this study is to evaluate industrial-scale batteries using GreenScreen® for Safer Chemicals, an established chemical hazard assessment (CHA) framework, and to develop a systematic, transparent methodology to quantify the CHA results, harmonize them, and aggregate them into single-value hazard scores, which can facilitate quantitative comparison and a robust evaluation of data gaps, inconsistencies, and uncertainty through the implementation of carefully selected scenarios and stochastic multicriteria acceptability analysis (SMAA). Using multiple authoritative toxicity data sources, six battery products are evaluated: three lithium-ion batteries (lithium iron phosphate, lithium nickel cobalt manganese hydroxide, and lithium manganese oxide), and three redox flow batteries (vanadium redox, zinc-bromine, and all-iron). The CHA results indicate that many materials in these batteries, including reagents and intermediates, inherently exhibit high hazard; therefore, safer materials should be identified and considered in future designs. The scenario analysis and SMAA, combined, provide a quantitative evaluation framework to support the decision-making needed to compare alternative technologies. Thus, this study highlights specific strategies to reduce the use of hazardous materials in complex engineered products before they are widely used in this rapidly-expanding industry sector.

Broad spectrum integration of climate change in health sciences curricula

In response to a University of California systemwide initiative to expand the knowledge base of climate change, two half-day workshops were held for faculty in the College of Health Sciences at the UC Irvine. In the first workshop, 20 participants who teach in the Schools of Nursing, Medicine, Pharmacy, and Pharmaceutical Science, or the Program in Public Health convened to explore concepts of sustainability, theoretical models of curriculum integration, challenges to adding new competencies into professional training, and strategies for integrating climate change modules and case studies into the curricula. The second half-day workshop was held a year after the first workshop to review how faculty members have modified their syllabus to integrate climate change information with varying degrees of success. A case study is presented regarding an asynchronous fully online course Introduction to Global Health, which is open to enrollment by students from all campuses of the University of California. The outcomes revealed preferential adoption of models of curriculum integration which minimized disruption of the sequence of topics in pre-existing courses. These include, for example, the use of longitudinal climate datasets for quantitative analysis of disease outcomes, and description of episodic events involving extreme weather conditions to explore differences in social determinants of vulnerability to climate change impacts in different populations. Integration of climate change as a distinct topic seems easier in elective courses in comparison with required courses designed to cover pre-established professional knowledge, competencies, and skills. The emergent requirement for interprofessional training in the health sciences provides an opportunity for the development of a cross-cutting competency domain including climate change as a unifying theme in a stand-alone course or set of courses in a sequenced model of curriculum integration.

Cultivating one health antibiotic stewards to bridge translational science gaps in the global action plan

Scientific evidence for the urgency of curbing the emergence and spread of antimicrobial resistance is incontrovertible. Yet, the translation of knowledge into effective design and implementation of action plans is hampered by gaps in perception, attitudes and practices in the human health, agriculture, and environmental sectors. To fill these gaps in regions where the disease burden attributable to antimicrobial resistance is heaviest, a cadre of One Health Stewards equipped with strategies to translate and meld global and local evidence for knowledge dissemination is deemed necessary. This opinion articulates a case for cultivating and deploying One Health Antibiotic Stewards according to specific actions within the environmental context of antibiotic resistance.

Toxic footprint and materials profile of electronic components in printed circuit boards

Waste printed circuit boards (WPCBs) contain valuable material resources and hazardous substances, thereby posing a challenge for sustainable resource recovery and environmental protection initiatives. Overcoming this challenge will require mapping the toxic footprint of WPCBs to specific materials and substances used in manufacturing electronic components (ECs). Therefore, this work collected 50 EC specimens from WPCBs in five ubiquitous consumer products, such as television, refrigerator, air conditioner, washing machine and computer. The work extracted and analyzed metal contents and used leachability assessments based on tests adopted by the regulatory policies from China and the United States. The work found that copper and iron are the most abundant constituents in ECs, with concentrations ranging 5.90-796.62 g/kg and 0-831.53 g/kg, respectively; whereas abundance of precious metal content is in the order of silver > gold > palladium > platinum, with silver concentration ranging 15-5290 mg/kg. The content of marginally-regulated toxic substance arsenic ranged 0-9700 mg/kg; whereas fully regulated toxic metals such as chromium, lead and mercury did not exceed the thresholds set by China and US standards. The work found new toxic threats from arsenic and selenium leached from 20 of 50 ECs exceeding regulatory standards. These results will aid manufacturers and recyclers in protecting workers' health and environmental quality from arsenic and selenium pollution, and should initiate discussion about regulating these toxic components as part of a comprehensive program to reduce the toxic footprint of electronic products.

Antibiotics stewardship in Ghana: a cross-sectional study of public knowledge, attitudes, and practices among communities

BACKGROUND

Antibiotic resistance is a major contributing factor to global morbidity and mortality and is associated with inappropriate medication use. However, the level of antibiotic consumption and knowledge about antibiotic resistance in Ghana is inadequately quantified. Our study identifies strategies for improved stewardship of antibiotics to prevent the proliferation of resistant pathogens by assessing the level of antibiotic knowledge, attitudes, and consumption behaviors by region, gender, age, and education in rural and urban Ghana.

METHODS

A cross-sectional study was conducted in 12 communities in the urban Greater Accra and rural Upper West regions of Ghana. A questionnaire survey was administered to 400 individuals aged 18 years and older in selected locations during September-October 2018 to collect data on individual knowledge, attitudes, and practices concerning antibiotics and antibiotic resistance. Multivariate analysis was used to investigate the association between demographic characteristics and knowledge, attitudes, and related behaviors.

RESULTS

Over 30% (125/400) had not received a doctor's prescription during their last illness. Seventy percent (278/400) had taken at least one antibiotic in the year prior to the survey. The top five frequently used antibiotics were Amoxicillin, Amoxicillin-clavulanic acid, Ampicillin, Ciprofloxacin, and Metronidazole. Women and older adults had higher knowledge compared to their respective counterparts (p < 0.01). Furthermore, prudent antibiotic use was significantly more prevalent in women than men (p < 0.05). Although no regional differences were found in overall knowledge, compared to urban residents, individuals residing in rural settings exhibited higher knowledge about the ineffectiveness of antibiotics for viruses like the cold and HIV/AIDS (p < 0.001). Two hundred and fifty-two (63%) respondents were unaware of antibiotic resistance. There was generally a low level of self-efficacy among participants regarding their role in preserving the effectiveness of antibiotics.

CONCLUSION

Antibiotic knowledge, attitudes, and use varied significantly across demographics, suggesting a context-specific approach to developing effective community interventions.

Thermal degradation and pollutant emission from waste printed circuit boards mounted with electronic components

Waste printed circuit boards mounted with electronic components (WPCB-ECs) are generated from electronic waste dismantling and recycling process. Air-borne pollutants, including particulate matter (PM) and volatile organic compounds (VOCs), can be released during thermal treatment of WPCB-CEs. In this study, organic substances from WPCB-ECs were pyrolyzed by both thermo-gravimetric analysis (TGA) and in a quartz tube furnace. We discovered that board resin and solder coating were degraded in a one-stage process, whereas capacitor scarfskin and wire jacket had two degradation stages. Debromination of brominated flame retardants occurred, and HBr and phenol were the main products during TGA processing of board resin. Dehydrochlorination occurred, and HCl, benzene and toluene were detected during the pyrolysis of capacitor scarfskin. Benzene formation was found only in the first degradation stage (272-372 °C), while toluene was formed both in the two degradation stages. PM with bimodal mass size distributions at diameters of 0.45-0.5 and 4-5 μm were emitted during heating WPCB-ECs. The PM number concentrations were highest in the size ranges of 0.3-0.35 μm and 1.6-2 μm. The research produced new data on pollutant emissions during thermal treatment of WPCB-ECs, and information on strategies to prevent toxic exposures that compromise the health of recyclers.

Toxicity trends in E-Waste: A comparative analysis of metals in discarded mobile phones

Mobile phones and various electronic products contribute to the world's fastest-growing category of hazardous waste with international repercussions. We investigated the trends in potential human health impacts and ecotoxicity of waste mobile phones through quantitative life cycle impact assessment (LCIA) methods and regulatory total threshold limit concentrations. A market-dominant sample of waste basic phones and smartphones manufactured between 2001 and 2015, were analyzed for toxicity trends based on 19 chemicals. The results of the LCIA (using USEtox model) show an increase in the relative mass of toxic materials over the 15-year period. We found no significant changes in the use of toxic components in basic phones, whereas smartphones contained a statistically significant increase in the content of toxic materials from 2006 to 2015. Nickel contributed the largest risk for carcinogens in mobile phones, but the contributions of lead and beryllium were also notable. Silver, zinc and copper contents were associated with non-cancer health risks. Copper components at 45,818-77,938 PAF m³/kg dominated ecotoxicity risks in mobile phones. Overall, these results highlight the increasing importance of monitoring trends in materials use for electronic product manufacturing and electronic-waste management processes that should prevent human and environmental exposures to toxic components.

Communicating Risk for a Climate-Sensitive Disease: A Case Study of Valley Fever in Central California

Valley Fever, or Coccidioidomycosis, a fungal respiratory disease, is prevalent with increasing incidence in the Southwestern United States, especially in the central region of California. Public health agencies in the region do not have a consistent strategy for communication and health promotion targeting vulnerable communities about this climate-sensitive disease. We used the behavior adaptation communication model to design and conduct semi-structured interviews with representatives of public health agencies in five California counties: Fresno, Kern, Kings, San Luis Obispo, and Tulare County. While none of the agencies currently include climate change information into their Valley Fever risk messaging, the agencies discuss future communication methods similar to other health risk factors such as poor air quality days and influenza virus season. For political reasons, some public health agencies deliberately avoided the use of climate change language in communicating health risk factors to farmers who are particularly vulnerable to soil and dust-borne fungal spores. The effectiveness of health communication activities of the public health agencies has not been measured in reducing the prevalence of Valley Fever in impacted communities. Given the transboundary nature of climate influence on Valley Fever risk, a concerted and consistent health communication strategy is expected to be more effective than current practices.

Emission characteristics and exposure assessment of particulate matter and polybrominated diphenyl ethers (PBDEs) from waste printed circuit boards de-soldering

Heating processes for the removal of electronic components from waste printed circuit boards (WPCBs) is an important step in the chain of electronic waste recycling, and toxic fumes are generated during the de-soldering process, causing environmental pollution and posing health risks for the workers. This study is aimed to characterize emission and deposition fluxes of respirable particulate matter (PM), and assess exposure of workers to particle-bound polybrominated diphenyl ethers (PBDEs). An electrical low-pressure impactor was used to measure the real-time PM concentrations inside and outside the hood during the WPCBs de-soldering process. The results show that PM mass concentration inside the hood (204 mg/m³) was significantly higher than outside the hood (9.4 mg/m³), representing 95.4% PM removal by the hood. According to the International Commission on Radiological Protection model, the total deposition fluxes of PM in head airways region, tracheobronchial region, and alveolar region were determined as 1930, 74.0, and 123 μg/h, respectively. The deposition flux for coarse particles (2.5-10 μm) in the head airways was the largest (1830 μg/h), accounting for 86.1% of total PM deposited in respiratory system. The ∑₈PBDEs concentration in PM₁₀ inside the WPCBs de-soldering workshop was 20,300 pg/m³, and the ∑₈PBDEs inhalation exposure for the worker was 1.46 ng/kg/day. This study improves understanding of PM emission mechanisms and provides fundamental data for health assessments during WPCBs de-soldering process.

Changes in Physical Activity After Installation of a Fitness Zone in a Community Park

Introduction

Increases in physical activity can lead to decreases in the prevalence of chronic diseases. Parks provide an ideal setting for physical activity. We investigated the effect of a fitness equipment installation on the intensity of park users’ physical activity at a community park.

Methods

We used the System for Observing Play and Recreation in a Community to record physical activity in Eastgate Park in Garden Grove, California, in August 2015 (preintervention [n = 1,650 person-periods]) and in February 2016 (postintervention [n = 1,776 person-periods]). We quantified physical activity in target areas of the park during 15-minute observation periods in 2 ways: 1) we categorized each user’s activity level during the period (sedentary, walking, vigorous), and 2) we converted activity levels to numeric metabolic equivalent task (MET) scores and calculated the period-average score across users. We used mixed-effects regression models to assess 1) the proportional odds of higher activity level at postintervention and 2) the association between intervention status (pre vs post) and mean period-average MET scores.

Results

In the immediate zone around the fitness equipment, the odds ratio for a higher activity level was 1.58 (95% confidence interval [CI], 1.14–2.18; P = .006) and the mean period-average MET score was 0.33 (95% CI, −0.07 to 0.74; P = .11) units higher at postintervention. Across the park as a whole, the odds ratio for a higher activity level was 1.41 (95% CI, 1.21–1.63; P < .001), and the mean period-average MET score was 0.34 (95% CI, 0.12–0.56; P = .003) units higher at postintervention.

Conclusion

Installing fitness zones appears to be an effective intervention for increasing physical activity of park users. Further studies need to be conducted to understand the sustained impact of fitness zones over time.

Spatiotemporal analysis of human exposure to halogenated flame retardant chemicals

Human exposure to flame retardants occurs in microenvironments due to their ubiquitous presence in consumer products and building materials. Recent research suggests higher levels of exposure through elevated surface dust (ESD) compared to floor dust (FD). However, it is unclear whether this pattern is consistent in different microenvironments beyond the home. We hypothesized that time spent in various microenvironments will significantly modify the pattern of human exposure to flame retardant chemicals in ESD and FD. We tested this hypothesis by collecting time activity diaries from 43 participants; and by estimating human exposure to 10 polybrominated diphenyl ether and 8 non-polybrominated diphenyl ether flame retardant chemicals, based on chemical concentrations measured in different microenvironments visited by the participants. The results of paired t-tests show that, with some notable exceptions, estimates of human exposure to most chemicals through ESD are statistically significantly higher for ∑PBDE (p=0.00) and ∑non-PBDEs (p=0.00) than through FD. This study reinforces the need to integrate temporal, locational, and elevation dimensions in assessing human exposure to potentially toxic flame retardant chemicals.

Potential human exposure to halogenated flame-retardants in elevated surface dust and floor dust in an academic environment

Most households and workplaces all over the world possess furnishings and electronics, all of which contain potentially toxic flame retardant chemicals to prevent fire hazards. Indoor dust is a recognized repository of these types of chemicals including polybrominated diphenyl ethers (PBDEs) and non-polybrominated diphenyl ethers (non-PBDEs). However, no previous U.S. studies have differentiated concentrations from elevated surface dust (ESD) and floor dust (FD) within and across microenvironments. We address this information gap by measuring twenty-two flame-retardant chemicals in dust on elevated surfaces (ESD; n=10) and floors (FD; n=10) from rooms on a California campus that contain various concentrations of electronic products. We hypothesized a difference in chemical concentrations in ESD and FD. Secondarily, we examined whether or not this difference persisted: (a) across the studied microenvironments and (b) in rooms with various concentrations of electronics. A Wilcoxon signed-rank test demonstrated that the ESD was statistically significantly higher than FD for BDE-47 (p=0.01), BDE-99 (p=0.01), BDE-100 (p=0.01), BDE-153 (p=0.02), BDE-154 (p=0.02), and 3 non-PBDEs including EH-TBB (p=0.02), BEH-TEBP (p=0.05), and TDCIPP (p=0.03). These results suggest different levels and kinds of exposures to flame-retardant chemicals for individuals spending time in the sampled locations depending on the position of accumulated dust. Therefore, further research is needed to estimate human exposure to flame retardant chemicals based on how much time and where in the room individuals spend their time. Such sub-location estimates will likely differ from assessments that assume continuous unidimensional exposure, with implications for improved understanding of potential health impacts of flame retardant chemicals.

Sensitivity of health sector indicators' response to climate change in Ghana

There is accumulating evidence that the emerging burden of global climate change threatens the fidelity of routine indicators for disease detection and management of risks to public health. The threat partially reflects the conservative character of the health sector and the reluctance to adopt new indicators, despite the growing awareness that existing environmental health indicators were developed to respond to risks that may no longer be relevant, and are too simplistic to also act as indicators for newer global-scale risk factors. This study sought to understand the scope of existing health indicators, while aiming to discover new indicators for building resilience against three climate sensitive diseases (cerebro spinal meningitis, malaria and diarrhea). Therefore, new potential indicators derived from human and biophysical origins were developed to complement existing health indicators, thereby creating climate-sensitive battery of robust composite indices of resilience in health planning. Using Ghana's health sector as a case study systematic international literature review, national expert consultation, and focus group outcomes yielded insights into the relevance, sensitivity and impacts of 45 indicators in 11 categories in responding to climate change. In total, 65% of the indicators were sensitive to health impacts of climate change; 24% acted directly; 31% synergistically; and 45% indirectly, with indicator relevance strongly associated with type of health response. Epidemiological indicators (e.g. morbidity) and health demographic indicators (e.g. population structure) require adjustments with external indicators (e.g. biophysical, policy) to be resilient to climate change. Therefore, selective integration of social and ecological indicators with existing public health indicators improves the fidelity of the health sector to adopt more robust planning of interdependent systems to build resilience. The study highlights growing uncertainties in translating research into protective policies when new indicators associated with non-health sources are needed to complement existing health indicators that are expected to respond to climate change.

Evolution of electronic waste toxicity: Trends in innovation and regulation

Rapid innovation in printed circuit board, and the uncertainties surrounding quantification of the human and environmental health impacts of e-waste disposal have made it difficult to confirm the influence of evolving e-waste management strategies and regulatory policies on materials. To assess these influences, we analyzed hazardous chemicals in a market-representative set of Waste printed circuit boards (WPCBs, 1996-2010). We used standard leaching tests to characterize hazard potential and USEtox® to project impacts on human health and ecosystem. The results demonstrate that command-and-control regulations have had minimal impacts on WPCBs composition and toxicity risks; whereas technological innovation may have been influenced more by resource conservation, including a declining trend in the use of precious metals such as gold. WPCBs remain classified as hazardous under U.S. and California laws because of excessive toxic metals. Lead poses the most significant risk for cancers; zinc for non-cancer diseases; copper had the largest potential impact on ecosystem quality. Among organics, acenaphthylene, the largest risk for cancers; naphthalene for non-cancer diseases; pyrene has the highest potential for ecotoxicological impacts. These findings support the need for stronger enforcement of international policies and technology innovation to implement the strategy of design-for-the-environment and to encourage recovery, recycling, and reuse of WPCBs.

Comparative study on copper leaching from waste printed circuit boards by typical ionic liquid acids

Waste printed circuit boards (WPCBs) are attracting increasing concerns because the recovery of its content of valuable metallic resources is hampered by the presence of hazardous substances. In this study, we used ionic liquids (IL) to leach copper from WPCBs. [BSO3HPy]OTf, [BSO3HMIm]OTf, [BSO4HPy]HSO4, [BSO4HMim]HSO4 and [MIm]HSO4 were selected. Factors that affect copper leaching rate were investigated in detail and their leaching kinetics were also examined with the comparison of [Bmim]HSO4. The results showed that all six IL acids could successfully leach copper out, with near 100% recovery. WPCB particle size and leaching time had similar influences on copper leaching performance, while IL acid concentration, hydrogen peroxide addition, solid to liquid ratio, temperature, showed different influences. Moreover, IL acid with HSO4(-) was more efficient than IL acid with CF3SO3(-). These six IL acids indicate a similar behavior with common inorganic acids, except temperature since copper leaching rate of some IL acids decreases with its increase. The results of leaching kinetics studies showed that diffusion plays a more important role than surface reaction, whereas copper leaching by inorganic acids is usually controlled by surface reaction. This innovation provides a new option for recovering valuable materials such as copper from WPCBs.

"Control-alt-delete": rebooting solutions for the E-waste problem

A number of efforts have been launched to solve the global electronic waste (e-waste) problem. The efficiency of e-waste recycling is subject to variable national legislation, technical capacity, consumer participation, and even detoxification. E-waste management activities result in procedural irregularities and risk disparities across national boundaries. We review these variables to reveal opportunities for research and policy to reduce the risks from accumulating e-waste and ineffective recycling. Full regulation and consumer participation should be controlled and reinforced to improve local e-waste system. Aiming at standardizing best practice, we alter and identify modular recycling process and infrastructure in eco-industrial parks that will be expectantly effective in countries and regions to handle the similar e-waste stream. Toxicity can be deleted through material substitution and detoxification during the life cycle of electronics. Based on the idea of "Control-Alt-Delete", four patterns of the way forward for global e-waste recycling are proposed to meet a variety of local situations.

Metallic Burden of Deciduous Teeth and Childhood Behavioral Deficits

Attention Deficit/Hyperactivity Disorder (ADHD) affects 5%–8% of children in the U.S. (10% of males and 4% of females). The contributions of multiple metal exposures to the childhood behavioral deficits are unclear, although particular metals have been implicated through their neurotoxicity. The objective of this study was to test the hypothesis that the body burden of Mn is positively correlated with ADHD symptoms. We also investigated the putative roles of Ca, Fe, Pb, and Hg. We collected shed molars from 266 children (138 boys and 128 girls) who lost a tooth between 11 and 13 years of age. The molars were analyzed for metals using ICP-OES. The third grade teacher of each child completed the Teacher’s Disruptive Behavior Disorders Rating Scale (DBD) to produce a score for “Total Disruptive Behavior” and subscale scores for “Attention Deficit Hyperactivity Disorder”, Hyperactivity/Impulsivity, Inattention, and Oppositional/Defiant. The mean Mn, Fe, Pb and Ca concentrations found in teeth was 3.1 ± 2.9 µg/g, 11.4 ± 12.1 µg/g, 0.5 ± 0.7 µg/g, and 3.0 × 10⁵ ± 0.8 × 10⁵ µg/g, respectively. Hg was not detected. No significant association was found between Mn and behavioral deficits. Ca was significantly negatively associated, and Pb showed a significant positive association with Hyperactivity/Impulsivity, Inattention, and Oppositional/Defiant Disorders. These findings call into question the putative independent association of manganese exposure and behavioral deficits in children, when the balance of other metallic burden, particularly Ca and Pb burdens play significant roles.

Toxic releases and risk disparity: a spatiotemporal model of industrial ecology and social empowerment

Information-based regulations (IBRs) are founded on the theoretical premise that public participation in accomplishing policy goals is empowered by open access to information. Since its inception in 1988, the Toxics Release Inventory (TRI) has provided the framework and regulatory impetus for the compilation and distribution of data on toxic releases associated with industrial development, following the tenets of IBR. As TRI emissions are reputed to disproportionately affect low-income communities, we investigated how demographic characteristics are related to change in TRI emissions and toxicity risks between 1989 and 2002, and we sought to identify factors that predict these changes. We used local indicators of spatial association (LISA) maps and spatial regression techniques to study risk disparity in the Los Angeles urban area. We also surveyed 203 individuals in eight communities in the same region to measure the levels of awareness of TRI, attitudes towards air pollution, and general environmental risk. We discovered, through spatial lag models, that changes in gross and toxic emissions are related to community ethnic composition, poverty level, home ownership, and base 1989 emissions (R-square=0.034-0.083). We generated a structural equation model to explain the determinants of social empowerment to act on the basis of environmental information. Hierarchical confirmatory factor analysis (HCFA) supports the theoretical model that individual empowerment is predicted by risk perception, worry, and awareness (Chi-square=63.315, p=0.022, df=42). This study provides strong evidence that spatiotemporal changes in regional-scale environmental risks are influenced by individual-scale empowerment mediated by IBRs.

Leaching assessments of toxic metals in waste plasma display panel glass

The plasma display panel (PDP) is rapidly becoming obsolete, contributing in large amounts to the electronic waste stream. In order to assess the potential for environmental pollution due to hazardous metals leached from PDP glass, standardized leaching procedures, chemical speciation assessments, and bioavailability tests were conducted. According to the Toxicity Characteristic Leaching Procedure (TCLP), arsenic in back glass was present at 4.46 ± 0.22 mg/L, close to its regulation limit of 5 mg/L. Zn is not available in the TCLP, but its TCLP leaching concentration in back glass is 102.96 ± 5.34 mg/L. This is because more than 90% of Zn is in the soluble and exchangeable and carbonate fraction. We did not detect significant levels of Ag, Ba, or Cu in the TCLP leachate, and the main fraction of Ag and Ba is residual, more than 95%, while the fraction distribution of Cu changes SEP by SEP. Ethylenediamine tetraacetic acid (EDTA)- and diethylenetriamine pentaacetic acid (DTPA)-extractable Ag, As, Ba, Cu, Zn, and Ni indicate a lower biohazards potential. These results show that, according to the EPA regulations, PDP glass may not be classified as hazardous waste because none of the metals exceeded their thresholds in PDP leachate. However, the concentrations of As and Zn should be lowered in the manufacturing process and finished product to avoid potential pollution problems.

IMPLICATIONS

The plasma display panel is rapidly becoming obsolete because of the liquid crystal display. In this study, the leachability of heavy metals contained in the waste plasma display panel glass was first examined by standardized leaching tests, typical chemical speciation assessments, and bioavailability tests, providing fundamental data for waste PDP glass recovery, recycling, and reuse.

Risks of toxic ash from artisanal mining of discarded cellphones

The potential environmental and human health impacts of artisanal mining of electronic waste through open incineration were investigated. A market-representative set of cellphones was dismantled into four component categories-batteries, circuit boards, plastics and screens. The components were shredded, sieved and incinerated at 743-818 °C. The concentrations of 17 metals were determined using U.S. EPA methods 6010C (inductively coupled plasma-atomic emission spectrometry; 6020A (inductively coupled plasma-mass spectrometry, or 7471B and 7470A (cold-vapor atomic absorption). EPA Method 8270 (gas chromatography/mass spectrometry) was used to identify polyaromatic hydrocarbon compounds and polybrominated diphenyl ethers. EPA Method 8082A was used to measure polychlorinated biphenyls and EPA Method 8290 was used for dioxin/furans in the residue ash. The life cycle assessment model USEtox(®) was used to estimate impacts of the ash residue chemicals on human health and the ecosystem. Among metals, copper in printed circuit boards had the highest ecotoxicity impact (1610-1930PAFm(3)/kg); Beryllium in plastics had the highest impact on producing non-cancer diseases (0.14-0.44 cases/kg of ash); and Nickel had the largest impact on producing cancers (0.093-0.35 cases/kg of ash). Among organic chemicals, dioxins from incinerated batteries produced the largest ecotoxicological impact (1.07E-04 to 3.64E-04PAFm(3)/kg). Furans in incinerated batteries can generate the largest number of cancers and non-cancer diseases, representing 8.12E-09 to 2.28E-08 and 8.96E-10 and 2.52E-09 cases/kg of ash, respectively. The results reveal hazards of burning discarded cellphones to recover precious metals, and pinpoints opportunities for manufacturers to reduce toxic materials used in specific electronic components marketed globally.

Dempster-Shafer theory applied to regulatory decision process for selecting safer alternatives to toxic chemicals in consumer products

Regulatory agencies often face a dilemma when regulating chemicals in consumer products-namely, that of making decisions in the face of multiple, and sometimes conflicting, lines of evidence. We present an integrative approach for dealing with uncertainty and multiple pieces of evidence in toxics regulation. The integrative risk analytic framework is grounded in the Dempster-Shafer (D-S) theory that allows the analyst to combine multiple pieces of evidence and judgments from independent sources of information. We apply the integrative approach to the comparative risk assessment of bisphenol-A (BPA)-based polycarbonate and the functionally equivalent alternative, Eastman Tritan copolyester (ETC). Our results show that according to cumulative empirical evidence, the estimated probability of toxicity of BPA is 0.034, whereas the toxicity probability for ETC is 0.097. However, when we combine extant evidence with strength of confidence in the source (or expert judgment), we are guided by a richer interval measure, (Bel(t), Pl(t)). With the D-S derived measure, we arrive at various intervals for BPA, with the low-range estimate at (0.034, 0.250), and (0.097,0.688) for ETC. These new measures allow a reasonable basis for comparison and a justifiable procedure for decision making that takes advantage of multiple sources of evidence. Through the application of D-S theory to toxicity risk assessment, we show how a multiplicity of scientific evidence can be converted into a unified risk estimate, and how this information can be effectively used for comparative assessments to select potentially less toxic alternative chemicals.

Mobility and efficacy of 2,4-D herbicide from slow-release delivery systems based on organo-zeolite and organo-bentonite complexes

This research aimed to develop slow-release formulations (SRFs) of 2,4-dichlorophenoxyacetic acid (2,4-D) using zeolite and bentonite minerals modified with cetyltrimethylammonium (CTMA) surfactant. Adsorption-desorption, greenhouse bioassay and column experiments were carried out to assess the potential of the SRFs to control weeds while reducing the herbicide leaching losses to deep layers of soil. The results showed that only 6.5 mmol 2,4-D kg(-1) was retained by Na-bent, and the herbicide was not adsorbed by Na-zeol at all. The surface modification with CTMA surfactant, however, improved the 2,4-D adsorption capacity of the zeolite and bentonite up to 207.5 and 415.8 mmol kg(-1), respectively. The synthesized organo-minerals slowly released the retained 2,4-D discharging 22 to 64% of the adsorbed 2,4-D to the solution phase within 7 days. The SRFs significantly (P = 0.05) reduced the herbicide mobility within the soil columns keeping a great portion of the herbicide active ingredient in the upper 5 cm soil layer. The SRFs were significantly (P = 0.05) as effective as the free technical herbicide in weed control without harming the ryegrass as the main plant. Therefore, the synthesized SRFs could be considered as useful tools for weed control in sustainable agriculture.

Electronic waste disassembly with industrial waste heat

Waste printed circuit boards (WPCBs) are resource-rich but hazardous, demanding innovative strategies for post-consumer collection, recycling, and mining for economically precious constituents. A novel technology for disassembling electronic components from WPCBs is proposed, using hot air to melt solders and to separate the components and base boards. An automatic heated-air disassembling equipment was designed to operate at a heating source temperature at a maximum of 260 °C and an inlet pressure of 0.5 MPa. A total of 13 individual WPCBs were subjected to disassembling tests at different preheat temperatures in increments of 20 °C between 80 and 160 °C, heating source temperatures ranging from 220 to 300 °C in increments of 20 °C, and incubation periods of 1, 2, 4, 6, or 8 min. For each experimental treatment, the disassembly efficiency was calculated as the ratio of electronic components released from the board to the total number of its original components. The optimal preheat temperature, heating source temperature, and incubation period to disassemble intact components were 120 °C, 260 °C, and 2 min, respectively. The disassembly rate of small surface mount components (side length ≤ 3 mm) was 40-50% lower than that of other surface mount components and pin through hole components. On the basis of these results, a reproducible and sustainable industrial ecological protocol using steam produced by industrial exhaust heat coupled to electronic-waste recycling is proposed, providing an efficient, promising, and green method for both electronic component recovery and industrial exhaust heat reutilization.

Comparative alternative materials assessment to screen toxicity hazards in the life cycle of CIGS thin film photovoltaics

Copper-indium-gallium-selenium-sulfide (CIGS) thin film photovoltaics are increasingly penetrating the market supply for consumer solar panels. Although CIGS is attractive for producing less greenhouse gas emissions than fossil-fuel based energy sources, CIGS manufacturing processes and solar cell devices use hazardous materials that should be carefully considered in evaluating and comparing net environmental benefits of energy products. Through this research, we present a case study on the toxicity hazards associated with alternative materials selection for CIGS manufacturing. We applied two numeric models, The Green Screen for Safer Chemicals and the Toxic Potential Indicator. To improve the sensitivity of the model outputs, we developed a novel, life cycle thinking based hazard assessment method that facilitates the projection of hazards throughout material life cycles. Our results show that the least hazardous CIGS solar cell device and manufacturing protocol consist of a titanium substrate, molybdenum metal back electrode, CuInS₂ p-type absorber deposited by spray pyrolysis, ZnS buffer deposited by spray ion layer gas reduction, ZnO:Ga transparent conducting oxide (TCO) deposited by sputtering, and the encapsulant polydimethylsiloxane.

Potential environmental and human health impacts of rechargeable lithium batteries in electronic waste

Rechargeable lithium-ion (Li-ion) and lithium-polymer (Li-poly) batteries have recently become dominant in consumer electronic products because of advantages associated with energy density and product longevity. However, the small size of these batteries, the high rate of disposal of consumer products in which they are used, and the lack of uniform regulatory policy on their disposal means that lithium batteries may contribute substantially to environmental pollution and adverse human health impacts due to potentially toxic materials. In this research, we used standardized leaching tests, life-cycle impact assessment (LCIA), and hazard assessment models to evaluate hazardous waste classification, resource depletion potential, and toxicity potentials of lithium batteries used in cellphones. Our results demonstrate that according to U.S. federal regulations, defunct Li-ion batteries are classified hazardous due to their lead (Pb) content (average 6.29 mg/L; σ = 11.1; limit 5). However, according to California regulations, all lithium batteries tested are classified hazardous due to excessive levels of cobalt (average 163,544 mg/kg; σ = 62,897; limit 8000), copper (average 98,694 mg/kg; σ = 28,734; limit 2500), and nickel (average 9525 mg/kg; σ = 11,438; limit 2000). In some of the Li-ion batteries, the leached concentrations of chromium, lead, and thallium exceeded the California regulation limits. The environmental impact associated with resource depletion and human toxicity is mainly associated with cobalt, copper, nickel, thallium, and silver, whereas the ecotoxicity potential is primarily associated with cobalt, copper, nickel, thallium, and silver. However, the relative contribution of aluminum and lithium to human toxicity and ecotoxicity could not be estimated due to insufficient toxicity data in the models. These findings support the need for stronger government policy at the local, national, and international levels to encourage recovery, recycling, and reuse of lithium battery materials.

Potential environmental impacts from the metals in incandescent, compact fluorescent lamp (CFL), and light-emitting diode (LED) bulbs

Artificial lighting systems are transitioning from incandescent to compact fluorescent lamp (CFL) and light-emitting diode (LED) bulbs in response to the U.S. Energy Independence and Security Act and the EU Ecodesign Directive, which leads to energy savings and reduced greenhouse gas emissions. Although CFLs and LEDs are more energy-efficient than incandescent bulbs, they require more metal-containing components. There is uncertainty about the potential environmental impacts of these components and whether special provisions must be made for their disposal at the end of useful life. Therefore, the objective of this study is to analyze the resource depletion and toxicity potentials from the metals in incandescent, CFL, and LED bulbs to complement the development of sustainable energy policy. We assessed the potentials by examining whether the lighting products are to be categorized as hazardous waste under existing U.S. federal and California state regulations and by applying life cycle impact-based and hazard-based assessment methods (note that "life cycle impact-based method" does not mean a general life cycle assessment (LCA) but rather the elements in LCA used to quantify toxicity potentials). We discovered that both CFL and LED bulbs are categorized as hazardous, due to excessive levels of lead (Pb) leachability (132 and 44 mg/L, respectively; regulatory limit: 5) and the high contents of copper (111,000 and 31,600 mg/kg, respectively; limit: 2500), lead (3860 mg/kg for the CFL bulb; limit: 1000), and zinc (34,500 mg/kg for the CFL bulb; limit: 5000), while the incandescent bulb is not hazardous (note that the results for CFL bulbs excluded mercury vapor not captured during sample preparation). The CFLs and LEDs have higher resource depletion and toxicity potentials than the incandescent bulb due primarily to their high aluminum, copper, gold, lead, silver, and zinc. Comparing the bulbs on an equivalent quantity basis with respect to the expected lifetimes of the bulbs, the CFLs and LEDs have 3-26 and 2-3 times higher potential impacts than the incandescent bulb, respectively. We conclude that in addition to enhancing energy efficiency, conservation and sustainability policies should focus on the development of technologies that reduce the content of hazardous and rare metals in lighting products without compromising their performance and useful lifespan.

International harmonization of models for selecting less toxic chemical alternatives: Effect of regulatory disparities in the United States and Europe

The desire to reduce human exposure to toxic chemicals associated with consumer products that are marketed globally demands the creation of comparative toxicity assessment tools that are based on uniform thresholds of acceptable risks and guidelines for materials use across international boundaries. The Toxic Potential Indicator (TPI) is a quantitative model based on European Union (EU) regulatory standards for toxicity and environmental quality. Here, we describe a version of TPI that we developed with US regulatory thresholds for environmental and human health impacts of toxic materials. The customized US-based TPI (USTPI) model integrates occupational permissible exposure limits (PELs), carcinogen categories based on the scheme of the International Agency for Research on Cancer (IARC), and median effect concentration for acute aquatic toxicity (EC50s). As a case study, we compare calculated scores for EU-based TPI (EUTPI) and USTPI for a large group of chemicals including 578 substances listed in the US Toxics Release Inventory (TRI). Statistical analyses show that the median difference between USTPI and EUTPI scores do not approximate to zero, implying a general discrepancy in TPI score results. Comparison of chemical ranking with Spearman's correlation coefficient suggests a positive but imperfect rank correlation. Although some discrepancies between EUTPI and USTPI may be explained by missing toxicity information in some regulatory categories, disparities between the 2 models are associated mostly with different input parameters, i.e., different regulatory thresholds and guidelines. These results demonstrate that regional differences in regulatory thresholds for material toxicity may compromise the ideals of international agreements, such as the Globally Harmonized System (GHS) of Classification and Labeling of Chemicals, and emphasis needs to be placed on eliminating inconsistencies in hazard assessment frameworks for substances.

Potential environmental impacts of light-emitting diodes (LEDs): metallic resources, toxicity, and hazardous waste classification

Light-emitting diodes (LEDs) are advertised as environmentally friendly because they are energy efficient and mercury-free. This study aimed to determine if LEDs engender other forms of environmental and human health impacts, and to characterize variation across different LEDs based on color and intensity. The objectives are as follows: (i) to use standardized leachability tests to examine whether LEDs are to be categorized as hazardous waste under existing United States federal and California state regulations; and (ii) to use material life cycle impact and hazard assessment methods to evaluate resource depletion and toxicity potentials of LEDs based on their metallic constituents. According to federal standards, LEDs are not hazardous except for low-intensity red LEDs, which leached Pb at levels exceeding regulatory limits (186 mg/L; regulatory limit: 5). However, according to California regulations, excessive levels of copper (up to 3892 mg/kg; limit: 2500), Pb (up to 8103 mg/kg; limit: 1000), nickel (up to 4797 mg/kg; limit: 2000), or silver (up to 721 mg/kg; limit: 500) render all except low-intensity yellow LEDs hazardous. The environmental burden associated with resource depletion potentials derives primarily from gold and silver, whereas the burden from toxicity potentials is associated primarily with arsenic, copper, nickel, lead, iron, and silver. Establishing benchmark levels of these substances can help manufacturers implement design for environment through informed materials substitution, can motivate recyclers and waste management teams to recognize resource value and occupational hazards, and can inform policymakers who establish waste management policies for LEDs.

How much e-waste is there in US basements and attics? Results from a national survey

The fate of used electronic products (e-waste) is of increasing concern because of their toxicity and the growing volume of e-waste. Addressing these concerns requires developing the recycling infrastructure, but good estimates of the volume of e-waste stored by US households are still unavailable. In this context, we make two contributions based on a national random survey of 2136 US households. First, we explain how much e-waste is stored by US households using count models. Significant explanatory variables include age, marital and employment status, ethnicity, household size, previous e-waste recycling behavior, and to some extent education, home ownership, and understanding the consequences of recycling, but neither income nor knowledge of e-waste recycling laws. Second, we estimate that on average, each US household has 4.1 small (<or=10 pounds) and 2.4 large e-waste items in storage. Although these numbers are likely lower bounds, they are higher than recent US Environmental Protection Agency (EPA) estimates (based on narrower product categories). This suggests that the backlog of e-waste in the US is likely larger than generally believed; it calls for developing the recycling infrastructure but also for targeted recycling campaigns.

Cost effectiveness of regulation-compliant filtration to control sediment and metal pollution in urban runoff

The implementation of Total Maximum Daily Load (TMDL) to control urban runoff presents major structural and managerial challenges for cities. We developed a decision support system (DSS) for TMDL compliance at the city level to solve for a phased, least-cost strategy toward meeting four TMDLs using stormwater filtration. Based on a case-study city, we modeled wet weather flows and associated discharge of Total Suspended Sediment (TSS), cadmium, copper, and zinc to receiving waters by coupling U.S. EPA's Storm Water Management Model (SWMM v. 5.0) with the geographic dataset of the urban drainage network. We linked a mixed integer linear programming algorithm to the watershed model for deriving cost-effective selection and placement of curb inlet filters to meet mass- and concentration-based TMDL requirements. The least cost solution for meeting the city's TMDL waste load allocations for TSS (73.9% reduction), Cd (50.6% reduction), Cu (30.0% reduction), and Zn (55.7% reduction) would require 1071 filter inserts at a cost of $1.7 million. In contrast, random placement of 1071 filters or uniform placement of 1266 filters is effective only for TSS and would cost $4.0 million and $4.8 million, respectively. Our results demonstrate the increases in cost-effectiveness of using an optimization-based DSS for urban watershed management.

Deposition of glomalin-related soil protein and sequestered toxic metals into watersheds

We hypothesized that glomalin-related soil proteins (GRSP) are eroded in sufficient quantities to influence metal loading into watersheds. We tested correlations among GRSP, Glomeromycota fungi, and metals (cadmium, iron, lead, and manganese) in proteins extracted from embankment soils at seven locations along an urban/coastal watershed. Immunoreactive (IRSP) and easily extractable (EE-IRSP) glomalin ranged from 0.007 to 2.9 mg g(-1) and from 0.006 to 0.63 mg g(-1) of soils, respectively. Glomalin-bound metals (microg mg(-1) protein) were Cd = 0.00-0.338; Fe = 0.5-227.7; Pb = 0.11-188.95; Mn = 2.23-784.42). Glomeromycota fungi were detected in 24% of all samples tested with PCR targeting the 18S and 28S ribosomal DNA extracted from soils. Specific assay for G. intraradices showed 3.08 x 10(7) copies g(-1) and 1.96 x 10(3) copies g(-1) of soil at two sites. Estimated annual glomalin loading into the watershed ranged from 5.48 x 10(2) to 7.22 x 10(4) kg of IRSP and from 2.57 x 102 to 2.86 x 10(4) kg of EE-IRSP; including 2.7 kg (Cd), 6.3 x 10(3) kg (Fe), 5.06 x 10(2) kg (Pb), and 1.80 x 10(3) kg (Mn). These data provide insights into the sources and ecological fate of a ubiquitous soil protein and its metals content.

Leaching assessments of hazardous materials in cellular telephones

Protocols for assessing the risks of discarded electronic products (e-waste) vary across jurisdictions, complicating the tasks of manufacturers and regulators. We compared the Federal Toxicity Characteristic Leaching Procedure (TCLP), California's Waste Extraction Test (WET), and the Total Threshold Limit Concentration (TTLC) on 34 phones to evaluate the consistency of hazardous waste classification. Our sample exceeded TCLP criteria only for lead (average 87.4 mg L(-1); range = 38.2-147.0 mg L(-1); regulatory limit = 5.0 mg L(-1), but failed TTLC for five metals: copper (average 203 g kg(-1); range = 186-224 g kg(-1); limit = 2.50 g kg(-1), nickel (9.25 g kg(-1); range = 6.34-11.20 g kg(-1); limit = 2.00 g kg(-1)), lead (10.14 g kg(-1); range = 8.2211.60 g kg(-1); limit = 1.00 g kg-1), antimony (1.02 g kg(-1); range = 0.86-1.29 g kg(-1); limit = 0.50 g kg(-1)), and zinc (11.01 g kg(-1); range = 8.82-12.80 g kg(-1); limit = 5.00 g kg(-1). Thresholds were not exceeded for WET. We detected several organic compounds, but at concentrations below standards. Brominated flame retardants were absent. These results improve existing environmental databases for e-waste and highlight the need to review regulatory testing for hazardous waste.

Modeling the environmental fate of manganese from methylcyclopentadienyl manganese tricarbonyl in urban landscapes

The environmental impacts of gasoline additives such as lead (Pb) and Methyl Tertiary Butyl Ether (MTBE) are well documented, leading to the phasing out of these additives. In contrast, little is known about the health and environmental impacts of potential replacement chemicals such as Methylcyclopentadienyl Manganese Tricarbonyl (MMT). The combustion of MMT in gasoline leads to the formation of MnPO4 and MnSO4 and MMT is considered a recent source of inorganic Mn in urban landscapes particularly in high traffic areas. The main objective of this study is to estimate the automotive deposition of Mn from MMT relative to the traffic volume at sites near a major highway in the Greater Toronto Area of Canada, where MMT is currently being used. Manganese emission levels were estimated for two sites that varied according to Annual Average Daily Traffic (AADT) density, fuel consumption, distance traveled by automobiles, and Mn concentration (mg l(-1)) in gasoline. Multiple regression analysis was used to predict the AADT volume from year 2002-2010. Comparison of the mass balance between the ANOVA means of 15% Mn emitted from the automobile tailpipes at 10, and 18 mg of Mn l(-1) in gasoline was conducted for both study sites. The percentage difference between the Mn input at the selected concentrations of Mn in gasoline and output into surface soil were found to be 99% significant for both sites. Thus the predicted 15% tailpipe emission levels for 10 mg of Mn l(-1) of gasoline used in automobiles, which represented 1290.03 g/year for site 1 and 555.94 g/year for site 2, will add 5.73 and 2.47 mg/kg of Mn annually, respectively. These input levels are considered negligible when compared to the natural abundance of Mn in soil. Based on these data, it could take more than 95-256 years of continuous MMT usage in the region to double the content of Mn in surface soils at the respective sites.

Topophilia and the quality of life

With this research I tested the hypothesis that individual preferences for specific ecosystem components and restorative environments are significantly associated with quality of life (QOL). A total of 379 human subjects responded to a structured 18-item questionnaire on topophilia and to the 26-item World Health Organization's Quality of Life (WHOQOL-Bref) instrument. Confirmatory factor analyses revealed four domains of topophilia (ecodiversity, synesthetic tendency, cognitive challenge, and familiarity) and four domains of QOL (physical, psychological, social, and environmental). Synesthetic tendency was the strongest domain of topophilia, whereas the psychological aspect of QOL was the strongest. Structural equation modeling was used to explore the adequacy of a theoretical model linking topophilia and QOL. The model fit the data extremely well: chi2 = 5.02, p = 0.414; correlation = 0.12 (p = 0.047). All four domains of topophilia were significantly correlated with the level of restoration experienced by respondents at their current domicile [for cognitive challenge: r = 0.19; p < 0.01; familiarity: r = 0.12; p < 0.05; synesthetic tendency: r = 0.18; p < 0.01; ecodiversity (the highest value): r = 0.28; p < 0.01]. Within ecodiversity, preferences for water and flowers were associated with high overall QOL (r = 0.162 and 0.105, respectively; p < 0.01 and 0.05, respectively). Within the familiarity domain, identifiability was associated with the environmental domain of QOL (r = 0.115; p < 0.05), but not with overall QOL. These results provide a new methodologic framework for linking environmental quality and human health and for implementing evidence-based provision of restorative environments through targeted design of built environments to enhance human QOL.

Manganese content of Tradescancia species exposed to automotive combustion of methylcyclopentadienyl manganese tricarbonyl in urban and rural landscapes

The purpose of this study is to assess the effect of manganese (Mn) from methylcyclopentadienyl manganese tricarbonyl (MMT) on grass (Tradescancia) species beside the major urban and rural highways in the greater Toronto area. Grass clippings were collected at distances up to 40 m from the roadside of a wooded, weakly exposed site (E+) and two unwooded, highly exposed sites (E++ and E+++) to Mn contamination. Statistical tests, including analysis of variance and correlation coefficients, were used to compare the Mn deposition on grass species with respect to distance and traffic density. A higher deposition of Mn was expected at the highly exposed sites when compared with the weakly exposed site, but a significantly higher concentration of Mn was observed at weakly exposed rural E+ site (Mn = 54.07 microg/g; dry wt) than the highly exposed urban E++ (Mn = 38.17 microg/g; dry wt) and E+++ (Mn = 35.63 microg/g; dry wt) sites. A significant correlation coefficient was found for Mn and traffic density (r2 = 0.311, p = 0.0074) at the weakly exposed site than at the highly exposed (r2 = 0.1589, p = 0.1052) urban sites. These data demonstrate that despite the continuous use of MMT in Canadian gasoline, the levels do not appear to exceed the worldwide tolerable levels (17-334 g/g; dry wt) in grass species inhabiting ecosystems next to major highways in urban regions.

Tetranucleotide frequencies in microbial genomes

A computational strategy for determining the variability of long DNA sequences in microbial genomes is described. Composite portraits of bacterial genomes were obtained by computing tetranucleotide frequencies of sections of genomic DNA, converting the frequencies to color images and arranging the images according to their genetic position. The resulting images revealed that the tetranucleotide frequencies of genomic DNA sequences are highly conserved. Sections that were visibly different from those of the rest of the genome contained ribosomal RNA, bacteriophage, or undefined coding regions and had corresponding differences in the variances of tetranucleotide frequencies and GC content. Comparison of nine completely sequenced bacterial genomes showed that there was a nonlinear relationship between variances of the tetranucleotide frequencies and GC content, with the highest variances occurring in DNA sequences with low GC contents (less than 0.30 mol). High variances were also observed in DNA sequences having high GC contents (greater than 0.60 mol), but to a much lesser extent than DNA sequences having low GC contents. Differences in the tetranucleotide frequencies may be due to the mechanisms of intercellular genetic exchange and/or processes involved in maintaining intracellular genetic stability. Identification of sections that were different from those of the rest of the genome may provide information on the evolution and plasticity of bacterial genomes.

Protein method for investigating mercuric reductase gene expression in aquatic environments

A colorimetric assay for NADPH-dependent, mercuric ion-specific oxidoreductase activity was developed to facilitate the investigation of mercuric reductase gene expression in polluted aquatic ecosystems. Protein molecules extracted directly from unseeded freshwater and samples seeded with Pseudomonas aeruginosa PU21 (Rip64) were quantitatively assayed for mercuric reductase activity in microtiter plates by stoichiometric coupling of mercuric ion reduction to a colorimetric redox chain through NADPH oxidation. Residual NADPH was determined by titration with phenazine methosulfate-catalyzed reduction of methyl thiazolyl tetrazolium to produce visible formazan. Spectrophotometric determination of formazan concentration showed a positive correlation with the amount of NADPH remaining in the reaction mixture (r2 = 0.99). Mercuric reductase activity in the protein extracts was inversely related to the amount of NADPH remaining and to the amount of formazan produced. A qualitative nitrocellulose membrane-based version of the method was also developed, where regions of mercuric reductase activity remained colorless against a stained-membrane background. The assay detected induced mercuric reductase activity from 10(2) CFU, and up to threefold signal intensity was detected in seeded freshwater samples amended with mercury compared to that in mercury-free samples. The efficiency of extraction of bacterial proteins from the freshwater samples was (97 +/- 2)% over the range of population densities investigated (10(2) to 10(8) CFU/ml). The method was validated by detection of enzyme activity in protein extracts of water samples from a polluted site harboring naturally occurring mercury-resistant bacteria. The new method is proposed as a supplement to the repertoire of molecular techniques available for assessing specific gene expression in heterogeneous microbial communities impacted by mercury pollution.

Protein Profile Variation in Cultivated and Native Freshwater Microorganisms Exposed to Chemical Environmental Pollutants

Assimilation of 35S-precursors into microbial proteins was used to investigate toxicity and adaptational responses that occur in nutrient enriched and natural freshwater samples experimentally contaminated with benzene, toluene, trichloroethylene (TCE), or xylene. Experiments were conducted to analyze (1) the potential of using microbial community protein profiles for responsive identification of chemical pollutant exposure, (2) the inhibition of microbial productivity through reduction in rate of protein synthesis caused by specific chemical pollutants, and (3) whether selection of subpopulations in freshwater microbial communities challenged with chemical pollutants leads to adaptive strategies mediated by production of particular polypeptides. The results show that distinct banding patterns of polypeptides in the range of 30 to 100 kilodaltons that were obtained following collective cultivation of freshwater microorganisms differ with each chemical pollutant. Protein yield and radioisotope incorporation were reduced within ten minutes of micro-bial exposure to chemical pollutants in the following order: xylene < toluene < benzene < TCE. Adaptation of the freshwater microbial community to chemical pollutants prior to radioisotope incorporation produced differences in polypeptide profiles, in the banding patterns of radioactive polypeptides, and in the rate of radioisotope incorporation. The rate of radioisotope incorporation by freshwater microorganisms pre-adapted to chemical pollutants was lowest with xylene (88.1% reduction), followed by TCE (84.0% reduction),toluene (67.3% reduction), and benzene (43.5% reduction). In long-term radioisotope incorporation experiments, protein yield and polypeptide radioactivity was higher in the presence of chemical pollutants than in uncontaminated control samples, suggesting increased metabolic productivity attributable to the chemical pollutants.