Translating antibiotic prescribing into antibiotic resistance in the environment: A hazard characterisation case study.

The environment receives antibiotics through a combination of direct application (e.g., aquaculture and fruit production), as well as indirect release through pharmaceutical manufacturing, sewage and animal manure. Antibiotic concentrations in many sewage-impacted rivers are thought to be sufficient to select for antibiotic resistance genes. Yet, because antibiotics are nearly always found associated with antibiotic-resistant faecal bacteria in wastewater, it is difficult to distinguish the selective role of effluent antibiotics within a 'sea' of gut-derived resistance genes. Here we examine the potential for macrolide and fluoroquinolone prescribing in England to select for resistance in the River Thames catchment, England. We show that 64% and 74% of the length of the modelled catchment is chronically exposed to putative resistance-selecting concentrations (PNEC) of macrolides and fluoroquinolones, respectively. Under current macrolide usage, 115 km of the modelled River Thames catchment (8% of total length) exceeds the PNEC by 5-fold. Similarly, under current fluoroquinolone usage, 223 km of the modelled River Thames catchment (16% of total length) exceeds the PNEC by 5-fold. Our results reveal that if reduced prescribing was the sole mitigating measure, that macrolide and fluoroquinolone prescribing would need to decline by 77% and 85%, respectively, to limit resistance selection in the catchment. Significant reductions in antibiotic prescribing are feasible, but innovation in sewage-treatment will be necessary for achieving substantially-reduced antibiotic loads and inactivation of DNA-pollution from resistant bacteria. Greater confidence is needed in current risk-based targets for antibiotics, particularly in mixtures, to better inform environmental risk assessments and mitigation.

Predicting risks from down-the-drain chemicals in a developing country: Mexico and linear alkylbenzene sulfonate as a case study.

It is recognized that the amount of natural dilution available can make a significant difference in the exposure and risk assessment of chemicals that emanate from wastewater treatment plants (WWTPs). However, data availability is a common limiting factor in exposure assessments for emerging markets. In the present study, we used a novel approach to derive dilution factors for the receiving waters within 5 km of wastewater discharge points in Mexico by combining locally measured river volumes, ecoregion categorization, data on WWTP capacity, and global river network models. Distributions of wastewater effluent into receiving stream dilution factors were developed for the entire country and organized by ecoregion type to explore spatial differences. The distribution of dilution factors in Mexico ranged from >1000 in tropical and temperate ecoregions to 1 in desert ecoregions. To demonstrate its utility, dilution factors were used to develop a probabilistic model to explore the potential ecological risks of the high-volume surfactant linear alkylbenzene sulfonate (LAS), commonly used in down-the-drain cleaning products. The predicted LAS river exposure values were below the predicted no-effect concentration in all regions. The methodology developed for Mexico can be used to derive refined exposure assessments in other countries with emerging markets throughout the world, resulting in more realistic risk assessments. Environ Toxicol Chem 2018;37:2475-2486. © 2018 SETAC.

Nano silver and nano zinc-oxide in surface waters - exposure estimation for Europe at high spatial and temporal resolution.

Nano silver and nano zinc-oxide monthly concentrations in surface waters across Europe were modeled at ~6 x 9 km spatial resolution. Nano-particle loadings from households to rivers were simulated considering household connectivity to sewerage, sewage treatment efficiency, the spatial distribution of sewage treatment plants, and their associated populations. These loadings were used to model temporally varying nano-particle concentrations in rivers, lakes and wetlands by considering dilution, downstream transport, water evaporation, water abstraction, and nano-particle sedimentation. Temporal variability in concentrations caused by weather variation was simulated using monthly weather data for a representative 31-year period. Modeled concentrations represent current levels of nano-particle production.Two scenarios were modeled. In the most likely scenario, half the river stretches had long-term average concentrations exceeding 0.002 ng L(-1) nano silver and 1.5 ng L(-1) nano zinc oxide. In 10% of the river stretches, these concentrations exceeded 0.18 ng L(-1) and 150 ng L(-1), respectively. Predicted concentrations were usually highest in July.

Worldwide estimation of river concentrations of any chemical originating from sewage-treatment plants using dilution factors.

Dilution factors are a critical component in estimating concentrations of so-called "down-the-drain" chemicals (e.g., pharmaceuticals) in rivers. The present study estimated the temporal and spatial variability of dilution factors around the world using geographically referenced data sets at 0.5° × 0.5° resolution. Domestic wastewater effluents were derived from national per capita domestic water use estimates and gridded population. Monthly and annual river flows were estimated by accumulating runoff estimates using topographically derived flow directions. National statistics, including the median and interquartile range, were generated to quantify dilution factors. Spatial variability of the dilution factor was found to be considerable; for example, there are 4 orders of magnitude in annual median dilution factor between Canada and Morocco. Temporal variability within a country can also be substantial; in India, there are up to 9 orders of magnitude between median monthly dilution factors. These national statistics provide a global picture of the temporal and spatial variability of dilution factors and, hence, of the potential exposure to down-the-drain chemicals. The present methodology has potential for a wide international community (including decision makers and pharmaceutical companies) to assess relative exposure to down-the-drain chemicals released by human pollution in rivers and, thus, target areas of potentially high risk.

Do natural rubber latex condoms pose a risk to aquatic systems?

The presence and potential adverse effects of plastic-polymers in the environment are receiving increasing attention in the popular and scientific press. However, quantifying emissions, exposure and effects of these materials remains a challenge. This paper describes the application of a questionnaire survey to quantify emissions of condom material from the domestic household to the sewage waste stream. Condoms are an important mainstay for birth control and the reduction of sexually transmitted infections. Survey participants were estimated to flush condoms down the toilet 2.96% of the time, and emissions were calculated as 0.99 mg of condom material per person per day. Using information on screening efficiencies at sewage treatment plants, the questionnaire data was combined with a GIS-based water quality model (LF2000-WQX) to predicted environmental concentrations (PEC) in a UK river basin catchment. Annual average PECs of condom material were 0.08-0.2 µg L(-1), under the model scenario used. To put these PECs into context, rubber latex condom material was degraded in outdoor microcosms. This resulted in the formation of a complex mixture of substances including chemical degradation products and particles in the nano range. The direct effects of the degradation mixture were investigated using two freshwater organisms with different life cycle traits, the water column crustacean Daphnia magna and the sediment-dwelling larval of Chironomus riparius. Ecotoxicity tests investigated both acute and chronic endpoints and were shown to exhibit no toxic effects. This precluded the derivation of a genuine no-effect concentration. Hence, the results suggest that limited risk to invertebrates is associated with latex condom degradation products to the organisms tested. Future studies should extend this risk framework to assess risks of condoms to other taxonomic groups as well as the risks of other polymer materials.

Assessing the ecotoxicologic hazards of a pandemic influenza medical response.

BACKGROUND: The global public health community has closely monitored the unfolding of the 2009 H1N1 influenza pandemic to best mitigate its impact on society. However, little attention has been given to the impact of this response on the environment. Antivirals and antibiotics prescribed to treat influenza are excreted into wastewater in a biologically active form, which presents a new and potentially significant ecotoxicologic challenge to microorganisms responsible for wastewater nutrient removal in wastewater treatment plants (WWTPs) and receiving rivers. OBJECTIVES: We assessed the ecotoxicologic risks of a pandemic influenza medical response. METHODS: To evaluate this risk, we coupled a global spatially structured epidemic model that simulates the quantities of antivirals and antibiotics used during an influenza pandemic of varying severity and a water quality model applied to the Thames catchment to determine predicted environmental concentrations. An additional model was then used to assess the effects of antibiotics on microorganisms in WWTPs and rivers. RESULTS: Consistent with expectations, our model projected a mild pandemic to exhibit a negligible ecotoxicologic hazard. In a moderate and severe pandemic, we projected WWTP toxicity to vary between 0-14% and 5-32% potentially affected fraction (PAF), respectively, and river toxicity to vary between 0-14% and 0-30% PAF, respectively, where PAF is the fraction of microbial species predicted to be growth inhibited (lower and upper 95% reference range). CONCLUSIONS: The current medical response to pandemic influenza might result in the discharge of insufficiently treated wastewater into receiving rivers, thereby increasing the risk of eutrophication and contamination of drinking water abstraction points. Widespread drugs in the environment could hasten the generation of drug resistance. Our results highlight the need for empirical data on the effects of antibiotics and antiviral medications on WWTPs and freshwater ecotoxicity.

A national risk assessment for intersex in fish arising from steroid estrogens.

The occurrence of intersex fish is widespread in the rivers of England and Wales. The extent of intersex in fish populations is believed to be strongly linked to their exposure to steroid estrogens. The present study presents, to our knowledge, the first national, catchment-based risk assessment for steroid estrogens in the world. A graphical information system-based model predicted the concentrations of estradiol (E2), estrone, and ethinylestradiol, which were combined and compared with known biological effect levels to predict the risk of endocrine disruption for 10,313 individual river reaches (21,452 km) receiving effluent from more than 2000 sewage treatment plants serving more than 29 million people. The large scale of this assessment underlines the usefulness of computer-based risk assessment methods. Overall, 61% [corrected] of the modeled reaches (all percentages are in terms of the total river length modeled) in England and Wales were predicted to be not at risk from endocrine disruption (mean concentrations, <1 ng/L E2 equivalents). A large range existed in the percentage of river reaches at risk in the various regions, from 5% in Wales to 67% in the Thames catchment. Important factors influencing this proportion are the population density, particularly their location, and the available dilution. A very small proportion of reaches (approximately 1-3%) were predicted to be at high risk (>10 ng/L E2 equivalents). Many of these high-risk reaches, however, were ditches, which were composed almost entirely of sewage effluent. The model could be applied equally well to any other chemical of concern emanating from the human population that would be impractical to assess by measurement.