Mutations are an important origin of antibiotic resistance in bacteria. While there is increasing evidence showing promoted resistance mutations by environmental stresses, no retrospective research has yet been conducted on this phenomenon and its mechanisms. Herein, we summarized the phenomena of stress-elevated resistance mutations in bacteria, generalized the regulatory mechanisms and discussed the environmental and human health implications. It is shown that both chemical pollutants, such as antibiotics and other pharmaceuticals, biocides, metals, nanoparticles and disinfection byproducts, and non-chemical stressors, such as ultraviolet radiation, electrical stimulation and starvation, are capable of elevating resistance mutations in bacteria. Notably, resistance mutations are more likely to occur under sublethal or subinhibitory levels of these stresses, suggesting a considerable environmental concern. Further, mechanisms for stress-induced mutations are summarized in several points, namely oxidative stress, SOS response, DNA replication and repair systems, RpoS regulon and biofilm formation, all of which are readily provoked by common environmental stresses. Given bacteria in the environment are confronted with a variety of unfavorable conditions, we propose that the stress-elevated resistance mutations are a universal phenomenon in the environment and represent a nonnegligible risk factor for ecosystems and human health. The present review identifies a need for taking into account the pollutants’ ability to elevate resistance mutations when assessing their environmental and human health risks and highlights the necessity of including resistance mutations as a target to prevent antibiotic resistance evolution.

Groundwater constitutes a major source of fresh water globally. However, it faces serious quality challenges from both conventional pollutants and contaminants of emerging concern (CECs) such as pharmaceutically active compounds (PhACs), personal care products (PCPs) and pesticides. There exists a significant knowledge gap regarding the occurrence of CECs in groundwater, especially in Africa. This study presents unique data on the concentration of fourteen PhACs, five PCPs and nine pesticides in groundwater wells in Nzoia River basin, Kenya. Generally, PCPs were the most dominant class with concentrations up to 10 μg/L (methylparaben). Anti(retro)virals, being important in the treatment of HIV/AIDS, were more prevalent among the PhACs as compared to the developed world, with concentrations up to 700 ng/L (nevirapine). In contrast, pesticides were measured at lower concentrations, the maximum being 42 ng/L (metolachlor). A basic risk assessment shows that – among the detected CECs – carbamazepine may pose medium human health risk and requires further investigation among infants and children. Point-of-use (POU) technologies are being increasingly promoted especially in the developing nations to provide drinking water solutions at the household level, but very little data is available on their performance towards CECs removal. Therefore, besides measuring CECs in groundwater, we investigated ceramic filters and solar disinfection (SODIS) as possible POU treatment options. Both techniques show potential to treat CECs in groundwater, with removal efficiencies higher than 90% obtained for 41 and 22 compounds in ceramic filters and SODIS, respectively. Moreover, for the more recalcitrant compounds (e.g. sulfadoxin), the performance is improved by up to three orders of magnitude when using TiO₂ as a photocatalyst in SODIS.

Legionella species are the etiological agent of Legionnaires' disease, a pathology easily contracted from water circuits and by the inhalation of aerosol droplets. This bacterium mainly proliferates in water: Legionella pneumophila is the most commonly isolated specie in water environments and consequently in water system, although further Legionella species have frequently been isolated, including Legionella dumoffii. The simultaneous presence of the two species in the water system can therefore lead to the simultaneous infection of several people, giving rise to harmful outbreaks. Ultraviolet inactivation of waterborne microorganisms offers a rapid and effective treatment technique and recently is getting more attention mostly to eliminate unsafe level of contamination. To tackle the issue, the inactivation of the two species of Legionella spp., namely L. pneumophila and L. dumoffii, by means of UV-A light emitting diodes (UV-A LED) system is explored. We used a commercially available UV-A LED at 365 nm wavelength, and the UV-A dose is given incrementally to the Legionellae with a concentration of 10⁶ CFU/mL in 0.9% NaCl (aq) solution. In this study, with a UV-A-dose of 1700 mJ/cm², the log-reduction of 3-log (99.9% inactivation) for L. pneumophila and 2.1-log (99.1% inactivation) for L. dumoffii of the contaminated water are achieved. The Electrical Energy per Order (EEO) is evaluated and showed this system is more economic and efficient in comparison with UV-C and UV-B LEDs. Following the support of this preliminary study with additional tests, aiming to validate the technology, we expect this device may be installed in water plants such as cooling systems or any water purification station in either industrial or home scales to reduce the risk of this infectious disease, preventing consumers' health.

Soil fumigation continues to play an important role in soil disinfection, but tools to significantly reduce emissions while providing environmental benefits (e.g., biochar) are lacking. The objective of this study was to determine the effects of biochar products on fumigant 1,3-dichloropropene (1,3-D) and chloropicrin (CP) emissions, their distribution and persistence in soil, nematode control, and potential toxicity to plants in a field trial. Treatments included three biochar products [two derived from almond shells (ASB) at either 550 or 900 °C pyrolysis temperature and one from coconut shells (CSB) at 550 °C] at 30 and 60 t ha⁻¹, a surface covering with a low permeability film (TIF), and no surface covering (control). A mixture of 1,3-D (∼65%) and CP (∼35%) was injected to ∼60 cm soil depth at a combined rate of 640 kg ha⁻¹. All biochar treatments significantly reduced emissions by 38–100% compared to the control. The ASB (900 °C) at both rates reduced emissions as effectively as the TIF (by 99–100%). Both fumigant emission reduction and residue in surface soil were positively correlated with biochar's adsorption capacity while cucumber germination rate and dry biomass were negatively correlated with residual fumigant concentrations in surface soil. This research demonstrated the potential and benefits of using biochar produced from local orchard feedstocks to control fumigant emissions. Additional research is needed to maximize the benefits of biochar on fumigant emission reductions without impacting plant growth.

Disinfection by-products (DBPs) are compounds produced during the water disinfection process. Iodoacetic acid (IAA) is one of the unregulated DBPs in drinking water, with potent cytotoxicity and genotoxicity in animals. However, whether IAA has toxic effects on oocyte maturation remains unclear. Here, we show that IAA exposure resulted in metaphase I (MI) arrest and polar-body-extrusion failure in mouse oocytes, indicating that IAA had adverse effects on mouse oocyte maturation in vitro. Particularly, IAA treatment caused abnormal spindle assembly and chromosome misalignment. Previous studies reported that IAA is a known inducer of oxidative stress in non-germline cells. Correspondingly, we found that IAA exposure increased the reactive oxygen species (ROS) levels in oocytes in a dose-dependent manner, indicating IAA exposure could induce oxidative stress in oocytes. Simultaneously, DNA damage was also elevated in the nuclei of these IAA-exposed mouse oocytes, evidenced by increased γ-H2AX focus number. In addition, the un-arrested oocytes entered metaphase II (MII) with severe defects in spindle morphologies and chromosome alignment after 14-h IAA treatment. An antioxidant, N-acetyl-L-cysteine (NAC), reduced the elevated ROS level and restored the meiotic maturation in the IAA-exposed oocytes, which indicates that IAA-induced maturation failure in oocytes was mainly mediated by oxidative stress. Collectively, our results indicate that IAA exposure interfered with mouse oocyte maturation by elevating ROS levels, disrupting spindle assembly, inducing DNA damage, and causing MI arrest.

Restoring woody vegetation to riparian zones helps to protect waterways from excessive sediment and nutrient inputs. However, the associated leaf litter can be a major source of dissolved organic matter (DOM) leached into surface waters. DOM can lead to the formation of disinfection by-products (DBPs) during drinking water treatment. This study investigated the DBPs formed during chlorination of DOM leached from leaf litter and assessed the potential toxicity of DBPs generated. We compared the leachate of two native Australian riparian trees, Casuarina cunninghamiana and Eucalyptus tereticornis, and a reservoir water source from a catchment dominated by Eucalyptus species. Leachates were diluted to dissolved organic carbon concentrations equivalent to the reservoir (~9 mg L⁻¹). E. tereticornis leachates produced more trihalomethanes (THMs), haloacetic acids (HAAs), and haloketones after chlorination, while C. cunninghamiana produced more chloral hydrate and haloacetonitriles. Leachate from both species produced less THMs and more HAAs per mole of carbon than reservoir water. This may be because reservoir water had more aromatic, humic characteristics while leaf leachates had relatively more protein-like components. Using in vitro bioassays to test the mixture effects of all chemicals, chlorinated E. tereticornis leachate induced oxidative stress in HepG2 liver cells and bacterial toxicity more frequently and at lower concentrations than C. cunninghamiana and reservoir water. Overall, this study has shown that the DOM leached from litter of these species has the potential to generate DBPs and each species has a unique DBP profile with differing bioassay responses. E. tereticornis may pose a relatively greater risk to drinking water than C. cunninghamiana as it showed greater toxicity in bioassays. This implies tree species should be considered when planning riparian zones to ensure the benefits of vegetation to waterways are not offset by unintended increased DBP production and associated toxicity following chlorination at downstream drinking water intakes.

Disinfection is considered as a vital step to ensure the supply of clean and safe drinking water. Various approaches are adopted for this purpose; however, chlorination is highly preferred all over the world. This method is opted owing to its several advantages. However, it leads to the formation of certain by-products. These chlorination disinfection by-products (DBPs) are genotoxic, carcinogenic and mutagenic. Still chlorination is being practiced worldwide. Present review gives insights into the occurrence, toxicity and factors affecting the formation of regulated (THMs, HAAs) and emerging DBPs (N-DBPs, HKs, HAs and aromatic DBPs) found in drinking water. Furthermore, remediation techniques used to control DBPs have also been summarized here. Key findings are: (i) concentration of regulated DBPs surpassed the permissible limit in most of the regions, (ii) high chlorine dose, high NOM, more reaction time (up to 3 h) and high temperature (up to 30 °C) enhance the formation of THMs and HAAs, (iii) high pH favors the formation of THMs while low pH is suitable of the formation of HAAs, (iv) high NOM, low temperature, low chlorine dose and moderate pH favors the formation of unstable DBPs (N-DBPs, HKs and HAs), (v) DBPs are toxic not only for humans but for aquatic fauna as well, (vi) membrane technologies, enhanced coagulation and AOPs remove NOM, (vii) adsorption, air stripping and other physical and chemical methods are post-formation approaches (viii) step-wise chlorination is assumed to be an efficient method to reduce DBPs formation without any treatment. Toxicity data revealed that N-DBPs are found to be more toxic than C-DBPs and aromatic DBPs than aliphatic DBPs. In majority of the studies, merely THMs and HAAs have been studied and USEPA has regulated just these two groups. Future studies should focus on emerging DBPs and provide information regarding their regulation.

Disinfection means the killing of pathogenic organisms (e.g. bacteria and its spores, viruses, protozoa and their cysts, worms, and larvae) present in water to make it potable for other domestic works. The substances used in the disinfection of water are known as disinfectants. At municipal level, chlorine (Cl₂), chloramines (NH₂Cl, NHCl₂), chlorine dioxide (ClO₂), ozone (O₃) and ultraviolet (UV) radiations, are the most commonly used disinfectants. Chlorination, because of its removal efficiency and cost effectiveness, has been widely used as method of disinfection of water. But, disinfection process may add several kinds of disinfection by-products (DBPs) (∼600–700 in numbers) in the treated water such as Trihalomethanes (THM), Haloacetic acids (HAA) etc. which are detrimental to the human beings in terms of cytotoxicity, mutagenicity, teratogenicity and carcinogenicity. In water, THMs and HAAs were observed in the range from 0.138 to 458 μg/L and 0.16–136 μg/L, respectively. Thus, several regulations have been specified by world authorities like WHO, USEPA and Bureau of Indian Standard to protect human health. Some techniques have also been developed to remove the DBPs as well as their precursors from the water. The popular techniques of DBPs removals are adsorption, advance oxidation process, coagulation, membrane based filtration, combined approaches etc. The efficiency of adsorption technique was found up to 90% for DBP removal from the water.

Recent reports are pointing towards the potential increasing risks of resistomes in human host. With no permissible limit in sight, resistomes are continually multiplying at an alarming rate in the ecosystem, with a disturbing level in drinking water source. The morphology and chemical constituent of resistomes afford them to resist degradation, elude membrane and counter ionic charge, thereby, rendering both conventional and advanced water and wastewater treatment inefficient. Water and wastewater matrix may govern the propagation of individual resistomes sub-type, co-selection and specific interaction towards precise condition may have enhanced the current challenge. This review covers recent reports (2011–2019) on the occurrence of ARB/ARGs and ease of spread of resistance genes in the aquatic ecosystem. The contributions of water matrix to the spread and mitigation, treatment options, via bulk removal or capture, and intracellular and extracellular DNA lysis were discussed. A complete summary of recent occurrences of ARB/ARGs, fate after disinfection and optimum conditions of individual treatment technology or in tandem, including process limitations, with a brief assessment of removal or degradation mechanism were highlighted.

Due to continuous spread of coronavirus disease 2019 (COVID-19) worldwide, long-term effective prevention and control measures should be adopted for public transport facilities, as they are increasing in popularity and serve as the principal modes for travel of many people. The human infection risk could be extremely high due to length of exposure time window, transmission routes and structural characteristics during travel or work. This can result in the rapid spread of the infection. Based on the transmission characteristics of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and the nature of public transport sites, we identified comprehensive countermeasures toward the prevention and control of COVID-19, including the strengthening of personnel management, personal protection, environmental cleaning and disinfection, and health education. Multi-pronged strategies can enhance safety of public transportation. The prevention and control of the disease during the use of public transportation will be particularly important when all countries in the world resume production. The aim of this study is to introduce experience of the prevention and control measures for public transportation in China to promote the global response to COVID-19.