Thomas J. McDonald

A review of the influence of treatment strategies on antibiotic resistant bacteria and antibiotic resistance genes.

Antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARG) in the aquatic environment have become an emerging contaminant issue, which has implications for human and ecological health. This review begins with an introduction to the occurrence of ARB and ARG in different environmental systems such as natural environments and drinking water resources. For example, ARG or ARB with resistance to ciprofloxacin, sulfamethoxazole, trimethoprim, quinolone, vancomycin, or tetracycline (e.g., tet(A), tet(B), tet(C), tet(G), tet(O), tet(M), tet(W), sul I, and sul II) have been detected in the environment. The development of resistance may be intrinsic, may be acquired through spontaneous mutations (de novo), or may occur due to horizontal gene transfer from donor bacteria, phages, or free DNA to recipient bacteria. An overview is also provided of the current knowledge regarding inactivation of ARB and ARG, and the mechanism of the effects of different disinfection processes in water and wastewater (chlorination, UV irradiation, Fenton reaction, ozonation, and photocatalytic oxidation). The effects of constructed wetlands and nanotechnology on ARB and ARG are also summarized.

Pharmaceuticals and personal care products in waters: occurrence, toxicity, and risk

Pharmaceuticals and personal care products (PPCP) are compounds with special physical and chemical properties that address the care of animal and human health. PPCP have been detected in surface water and wastewater in the ng/L to µg/L concentration range worldwide. PPCP ecotoxicity has been studied in a variety of organisms, and multiple methods have been used to assess the risk of PPCP in the environment to ecological health. Here we review the occurrence, effects, and risk assessment of PPCP in aquatic systems, as well as the sustainability of current methods for managing PPCP contamination in aquatic systems. The major points are the following: (1) a number of PPCP present potential concerns at environmentally relevant concentrations. PPCP mixtures may produce synergistic toxicity. (2) Various methods have been used for the ecological risk assessment of PPCP in aquatic systems. There are similarities in these methods, but no consensus has emerged regarding best practices for the ecological risk assessment of these compounds. (3) Human health risk assessments of PPCP contamination in aquatic systems have generally indicated little cause for concern. However, there is a lack of information regarding whether antibiotic contamination in wastewater and aquatic systems could lead to an increase in clinically relevant antibiotic-resistant bacteria and antibiotic-resistant genes. (4) Over the next century, the combination of increasing global population size and potential droughts may result in reduced water availability, increased need for water reuse, and increasing concentrations of PPCP in wastewaters. The current wastewater treatment methods do not remove all PPCP effectively. This, coupled with the possibility that antibiotics may promote the development of antibiotic-resistant bacteria and antibiotic-resistant genes, leads to concerns about the sustainability of global water supplies.

Formation and toxicity of brominated disinfection byproducts during chlorination and chloramination of water: a review.

Disinfection byproducts (DBPs) in drinking water exhibit considerable adverse health effects; recent focus is on the brominated disinfection byproducts (Br-DBPs). The chlorination and chloramination of bromide ion containing water produce reactive bromo species, which subsequently react with natural organic matter (NOM) to yield Br-DBPs. The possible reactions involved in generating DBPs are presented. Identified Br-DBPs include bromomethanes, bromoacetic acid, bromoacetamides, bromoacetonitriles, and bromophenols. Mixed chloro- and bromo-species have also been identified. Pathways of the formation of Br-DBPs have been described. The concentration of Br− ion, pH, reaction time, and the presence of Cu(II) influence the yield of DBPs. The effects of water conditions on the production of Br-DBPs are presented. The epidemiological studies to understand the potential toxic effects of DBPs including Br-DBPs are summarized. Brominated DBPs may have higher health risks than their corresponding chlorinated DBPs. A potential role of an emerging alternate disinfectant, ferrate (FeVIO2− 4), in minimizing DBPs is briefly discussed.

Magnetic graphene-carbon nanotube iron nanocomposites as adsorbents and antibacterial agents for water purification.

One of the biggest challenges of the 21st century is to provide clean and affordable water through protecting source and purifying polluted waters. This review presents advances made in the synthesis of carbon- and iron-based nanomaterials, graphene-carbon nanotubes-iron oxides, which can remove pollutants and inactivate virus and bacteria efficiently in water. The three-dimensional graphene and graphene oxide based nanostructures exhibit large surface area and sorption sites that provide higher adsorption capacity to remove pollutants than two-dimensional graphene-based adsorbents and other conventional adsorbents. Examples are presented to demonstrate removal of metals (e.g., Cu, Pb, Cr(VI), and As) and organics (e.g., dyes and oil) by grapheme-based nanostructures. Inactivation of Gram-positive and Gram-negative bacterial species (e.g., Escherichia coli and Staphylococcus aureus) is also shown. A mechanism involving the interaction of adsorbents and pollutants is briefly discussed. Magnetic graphene-based nanomaterials can easily be separated from the treated water using an external magnet; however, there are challenges in implementing the graphene-based nanotechnology in treating real water.

Biogeochemistry of selenium. A review

Selenium levels and speciation in environmental compartments and the dynamics of global Se cycling continue to be a subject of intense interest largely because Se is both an essential element and a toxicant at elevated levels. While Se containing amino acids and proteins are known to be critical for normal metabolic functions in many life forms, selenosis, poisoning due to chronic excessive Se intake, has been associated with neurological impairment. This paper reviews the current understanding of the biogeochemistry of selenium in the natural environment. The factors that affect Se speciation in natural environments are chemical, physical, and biological processes. Several inorganic species of Se (−2, 0, +4, and +6) and organic species (monomethylated and dimethylated) have been reported in aquatic systems. Both HSeO3− and SeO32− would be present in natural waters. Under mild oxidizing conditions, HSeO3− and SeO32− are the major species, while HSe− would be the dominant species at pH greater than 4 and strong reducing conditions. The biogeochemistry of selenium is discussed in terms of variation of speciation with pH and redox conditions, sorption on solid surfaces, role of reducing species under oxic/anoxic conditions, and interaction with natural organic matter.

Mechanistic relationships between hepatic genotoxicity and carcinogenicity in male B6C3F1 mice treated with polycyclic aromatic hydrocarbon mixtures.

Abstract The genotoxicity of a complex mixture [neutral fraction (NF)] from a wood preserving waste and reconstituted mixturexa0(RM) mimicking the NF with seven major polycyclic aromatic hydrocarbons (PAHs) and benzo(a)pyrene (BaP) was investigated by determining DNA adducts and tumor incidence in male B6C3F1 mice exposed to three different doses of the chemical mixtures. The peak values of DNA adducts were observed after 24xa0h, and the highest levels of PAH–DNA adducts were exhibited in mice administered NFxa0+xa0BaP, and the highest tumor incidence and mortality were also observed in this group. DNA adduct levels after 1, 7, or 21xa0days were significantly correlated with animal mortality and incidence of total tumors including liver, lung, and forestomach. However, only hepatic DNA adducts after 7xa0days significantly correlated with liver tumor incidence. Most proteins involved in DNA repair including ATM, pATR, Chk1, pChk1, DNA PKcs, XRCC1, FANCD2, Ku80, Mre11, and Brca2 were significantly lower in liver tumor tissue compared to non-tumor tissue. Expressions of proteins involved in apoptosis and cell cycle regulation were also significantly different in tumor versus non-tumor tissues, and it is possible that PAH-induced changes in these gene products are important for tumor development and growth.

Biomarker measurements of prenatal exposure to polychlorinated biphenyls (PCB) in umbilical cord blood from postpartum Hispanic women in Brownsville, Texas.

Biomarkers of polychlorinated biphenyls (PCB) were measured in both maternal and umbilical cord blood from 35 pregnant Hispanic women living in Brownsville, TX. Gas chromatography with an electron capture detector (GC/ECD) was used to analyze for 22 PCB analytes. Results indicated that both pregnant mothers and their fetuses were exposed to a variety of PCB at relatively low levels (≤0.2 ng/ml), and that concentrations in maternal and cord blood were similar. Concentrations of total PCB (sum or all PCB congeners) averaged more than 2.5 ng/ml, with highest values exceeding 3 ng/ml. Although health implications are uncertain, reports in the literature of PCB-related health effects raise concerns about possible future health consequences, especially obesity and diabetes, in this potentially vulnerable population.

Confirming the Environmental Concerns of Community Members Utilizing Participatory-Based Research in the Houston Neighborhood of Manchester

In the last few decades, there has been an increase in community-based participatory research being conducted within the United States. Recent research has demonstrated that working with local community organizations, interest groups, and individuals can assist in the creation of, and sustainability in, health initiatives, adoption of emergency protocols, and potentially improve health outcomes for at-risk populations. However little research has assessed if communal concerns over environmental contaminants would be confirmed through environmental research. This cross-sectional study collected survey data and performed surface water analysis for heavy metals in a small neighborhood in Houston, TX, which is characterized by industrial sites, unimproved infrastructure, nuisance flooding, and poor air quality. Surveys were completed with 109 residents of the Manchester neighborhood. Water samples were taken from thirty zones within the neighborhood and assessed for arsenic (As), barium (Ba), cadmium (Cd), chromium (Cr), lead (Pb), selenium (Se), silver (Ag), and mercury (Hg). Survey results showed that the vast majority of all respondents were concerned over proximity to industry and waste facilities, as well as exposure to standing surface water. Barium was discovered in every sample and many of the zones showed alarming levels of certain metals. For example, one zone, two blocks from a public park, showed levels of arsenic at 180 (μg/L), barium at 3296 (μg/L), chromium at 363 (μg/L), lead at 1448 (μg/L), and mercury at 10 (μg/L). These findings support the hypothesis that neighborhood members are aware of the issues affecting their community and can offer researchers valuable assistance in every stage of study design and execution.

Measurement of Organophosphate Pesticides, Organochlorine Pesticides, and Polycyclic Aromatic Hydrocarbons in Household Dust from Two Rural Villages in Nepal

Although there are few published studies of residential exposures to environmental contaminants in Nepal, there may be substantial exposures to multiple contaminants in Nepali households. Pesticides, which can be harmful to human health, are often used by Nepali farmers, and many farmers lack an understanding of the appropriate procedures for the safe use, handling and storage of pesticides. In addition, many Nepali families use wood burning stoves, leading to the potential for exposure to polycyclic aromatic hydrocarbons from wood smoke. This study measured the levels of four organophosphate pesticides, 22 organochlorine pesticides, and over thirty polycyclic aromatic hydrocarbons in house dust from two rural Nepali villages. Floor dust samples were collected in early summer from a total of 18 households, including nine households in the village of Keraghari, in Kavrepalanchok District, and nine homes in the village of Kafaldanda, in Lalitpur District. These villages have similar environmental features and are located at an altitude of approximately 2,000 meters. In these two villages, many of the homes have improved cookstoves to reduce smoke levels in the homes. The dust samples were collected using pre-ashed glass fiber filter cloths saturated with isopropyl alcohol. In both villages, the organochlorine pesticide that was present in the highest concentrations was the DDT metabolite p,p’-dichlorodiphenyldichloroethylene (4,4’-DDE). Among the organophosphates, methyl parathion accounted for much of the organophosphate mass detected. Across both villages, the median total organochlorine pesticide value (287 ng/m2) was 5-fold higher than the median total organophosphate pesticide value (54.3 ng/m2). The median total polycyclic aromatic hydrocarbon concentration in house dust from both villages was 14,700 ng/m2. Interventions are needed to improve safe handling and use of pesticides in Nepali villages. Additional studies are also needed to assess the extent to which improved cookstoves reduce polycyclic aromatic hydrocarbon exposure, during both winter and summer.

Nitrosatable Drug Exposure during Pregnancy and Preterm and Small‐for‐Gestational‐Age Births

BACKGROUNDnNitrosatable drugs react with nitrite in the stomach to form N-nitroso compounds, observed in animal models to result in adverse pregnancy outcomes, such as birth defects and reduced fetal weight. Previous studies examining prenatal exposure to medications classified as nitrosatable have reported an increased risk of preterm births (PTBs) and small-for-gestational-age (SGA) infants.nnnMETHODSnUsing data from mothers (controls) of babies without major birth defects from the National Birth Defects Prevention Study, prenatal nitrosatable drug usage by trimester and month of gestation was examined in relation to PTBs and SGA infants.nnnRESULTSnPositive associations were observed with nitrosatable drug use and PTBs, with the strongest relationship with second trimester exposure (adjusted hazard ratio [aHR] 1.37, [95% confidence interval (CI) 1.10, 1.70]). Of the nitrosatable functional groups, secondary amines were the most notable, with a higher association among women with second (aHR 1.37, [95% CI 1.05, 1.79]) and third (aHR 1.34, [95% CI 1.02, 1.76]) trimester exposure compared with women with no prenatal nitrosatable drug use. Among SGA infants, a borderline association was noted with amide exposure during the third trimester (adjusted odds ratio 1.43 [95% confidence interval [CI] 1.00, 2.05]).nnnCONCLUSIONSnPrenatal exposure to nitrosatable drugs during the second and third trimester of pregnancy, particularly secondary amines, might increase the risk of PTBs. However, prenatal exposure to nitrosatable drugs was not associated with SGA infants, with the exception of amide drugs.