M.J. Whelan

Consideration of exposure and species sensitivity of triclosan in the freshwater environment

ABSTRACT Triclosan (TCS) is a broad-spectrum antimicrobial used in consumer products including toothpaste and hand soap. After being used, TCS is washed or rinsed off and residuals that are not biodegraded or otherwise removed during wastewater treatment can enter the aquatic environment in wastewater effluents and sludges. The environmental exposure and toxicity of TCS has been the subject of various scientific and regulatory discussions in recent years. There have been a number of publications in the past 5 y reporting toxicity, fate and transport, and in-stream monitoring data as well as predictions from aquatic risk assessments. State-of-the-science probabilistic exposure models, including Geography-referenced Regional Exposure Assessment Tool for European Rivers (GREAT-ER) for European surface waters and Pharmaceutical Assessment and Transport Evalutation (PhATE™) for US surface waters, have been used to predict in-stream concentrations (PECs). These models take into account spatial and temporal variability in river flows and wastewater emissions based on empirically derived estimates of chemical removal in wastewater treatment and in receiving waters. These model simulations (based on realistic use levels of TCS) have been validated with river monitoring data in areas known to be receiving high wastewater loads. The results suggest that 90th percentile (low flow) TCS concentrations are less than 200 ng/L for the Aire–Calder catchment in the United Kingdom and between 250 ng/L (with in-stream removal) and 850 ng/L (without in-stream removal) for a range of US surface waters. To better identify the aquatic risk of TCS, a species sensitivity distribution (SSD) was constructed based on chronic toxicity values, either no observed effect concentrations (NOECs) or various percentile adverse effect concentrations (EC10–25 values) for 14 aquatic species including fish, invertebrates, macrophytes, and algae. The SSD approach is believed to represent a more realistic threshold of effect than a predicted no effect concentration (PNEC) based on the data from the single most sensitive species tested. The log-logistic SSD was used to estimate a PNEC, based on an HC5,50 (the concentration estimated to affect the survival, reproduction and/or growth of 5% of species with a 50% confidence interval). The PNEC for TCS was 1,550 ng/L. Comparing the SSD-based PNEC with the PECs derived from GREAT-ER and PhATE modeling to simulate in-river conditions in Europe and the United States, the PEC to PNEC ratios are less than unity suggesting risks to pelagic species are low even under the highest likely exposures which would occur immediately downstream of wastewater treatment plant (WWTP) discharge points. In-stream sorption, biodegradation, and photodegradation will further reduce pelagic exposures of TCS. Monitoring data in Europe and the United States corroborate the modeled PEC estimates and reductions in TCS concentrations with distance downstream of WWTP discharges. Environmental metabolites, bioaccumulation, biochemical responses including endocrine-related effects, and community level effects are far less well studied for this chemical but are addressed in the discussion. The aquatic risk assessment for TCS should be refined as additional information becomes available.

Determination of decamethylcyclopentasiloxane in river water and final effluent by headspace gas chromatography/mass spectrometry

A method is described for the analysis of decamethylcyclopentasiloxane (D(5)) in river water and treated waste water using headspace gas chromatography/mass spectrometry. Internal standard addition to samples and field blanks was carried out in the field to provide both a measure of recovery and to prevent any exposure of samples to laboratory air, which contained background levels of D(5). Measured levels of D(5) were typically in the range <10-29ngL(-1) in the River Great Ouse (UK) with slightly higher levels in the River Nene (UK). The measured concentration of D(5) in treated waste water varied between 31 and 400ngL(-1), depending on the type of treatment process employed.

Modelling spatial patterns of throughfall and interception loss in a Norway spruce (Picea abies) plantation at the plot scale

Abstract The estimation of throughfall to forest systems is an important requirement for modelling the hydrology and chemistry of catchments and for understanding moisture dependent processes on the forest floor. Despite widespread recognition that throughfall is inherently variable, relatively few attempts have been made to account for any systematic influence canopy architecture may have over throughfall patterns. A simple Rutter-type interception model is developed here to include spatially distributed parameters which are related to variable canopy cover and interception capacity. Evaporation rates are approximated using the Penman-Monteith equation and canopy drainage is modelled using a negative exponential equation related to canopy wetness. The model was calibrated and validated using field observations of throughfall from a regular array of funnel collectors installed in a small plot in a Norway spruce ( Picea abies ) plantation in southwest England. The observed throughfall patterns had a strong systematic component which was strongly correlated with spatially distributed measured canopy cover and calibrated canopy capacity. The model was able to reproduce the broad trends in observed patterns of throughfall to the plot and was able to predict the cumulative total throughfall input to the plot over 77 days to within 2% of the measured input.

Nitrate pollution in intensively farmed regions: What are the prospects for sustaining high‐quality groundwater?

[1] Widespread pollution of groundwater by nutrients due to 20th century agricultural intensification has been of major concern in the developed world for several decades. This paper considers the River Thames catchment (UK), where water-quality monitoring at Hampton (just upstream of London) has produced continuous records for nitrate for the last 140 years, the longest continuous record of water chemistry anywhere in the world. For the same period, data are available to characterize changes in both land use and land management at an annual scale. A modeling approach is used that combines two elements: an estimate of nitrate available for leaching due to land use and land management; and, an algorithm to route this leachable nitrate through to surface or groundwaters. Prior to agricultural intensification at the start of World War II, annual average inputs were around 50 kg ha−1, and river concentrations were stable at 1 to 2 mg l−1, suggesting in-stream denitrification capable of removing 35 (±15) kt N yr−1. Postintensification data suggest an accumulation of 100 (±40) kt N yr−1 in the catchment, most of which is stored in the aquifer. This build up of reactive N species within the catchments means that restoration of surface nitrate concentrations typical of the preintensification period would require massive basin-wide changes in land use and management that would compromise food security and take decades to be effective. Policy solutions need to embrace long-term management strategies as an urgent priority.

Nitrate in United Kingdom Rivers: Policy and Its Outcomes Since 1970

Modern conventional farming provides Western Europe and North America with reliable, high quality, and relatively cheap supplies of food and fiber, increasingly viewed as a potential source of fuel. One of the costs is continued widespread pollution of rivers and groundwater-predominantly by nutrients. In 1970, in both the United States and UK, farming was focused on maximizing yield and management practices were rapidly modernizing. Little attention was paid to the external impacts of farming. In 2010, diffuse pollution from agriculture is being seriously addressed by both voluntary and statutory means in an attempt to balance environmental costs with the continued benefits of agricultural production. In this paper we consider long-term changes in the concentration and flux of nitrate in five rural UK rivers to demonstrate the impact of agricultural intensification and subsequent policies to reduce diffuse pollution on river water quality between 1970 and 2010.

An assessment of the risk to surface water ecosystems of groundwater P in the UK and Ireland

A good quantitative understanding of phosphorus (P) delivery is essential in the design of management strategies to prevent eutrophication of terrestrial freshwaters. Most research to date has focussed on surface and near-surface hydrological pathways, under the common assumption that little P leaches to groundwater. Here we present an analysis of national patterns of groundwater phosphate concentrations in England and Wales, Scotland, and the Republic of Ireland, which shows that many groundwater bodies have median P concentrations above ecologically significant thresholds for freshwaters. The potential risk to receptor ecosystems of high observed groundwater P concentrations will depend on (1) whether the observed groundwater P concentrations are above the natural background; (2) the influence of local hydrogeological settings (pathways) on the likelihood of significant P transfers to the receptor; (3) the sensitivity of the receptor to P; and, (4) the relative magnitude of P transfers from groundwater compared to other P sources. Our research suggests that, although there is often a high degree of uncertainty in many of these factors, groundwater has the potential to trigger and/or maintain eutrophication under certain scenarios: the assumption of groundwater contribution to river flows as a ubiquitous source of dilution for P-rich surface runoff must therefore be questioned. Given the regulatory importance of P concentrations in triggering ecological quality thresholds, there is an urgent need for detailed monitoring and research to characterise the extent and magnitude of different groundwater P sources, the likelihood for P transformation and/or storage along aquifer-hyporheic zone flow paths and to identify the subsequent risk to receptor ecosystems.

Variability in the quality of Pinus sylvestris needles and litter from sites with different soil characteristics: Lignin and phenylpropanoid signature

Abstract Intact Pinus sylvestris needles and litter from the soil surface were sampled from several stands in SW England growing on soils with different chemical characteristics. The intrinsic chemical and biochemical characteristics of needle and litter samples were measured. The total concentration of lignin, measured by proximate analysis, and the chemical characteristics of the lignin-polymer in P. sylvestris needles and litter, varied between soil types. Lignin concentrations increased from 180 to 316 mg litter g −1 with increasing soil base saturation, although no similar trends in the concentration of lignin in needles were observed. The total concentration of phenylpropanoid moieties, released on CuO-oxidation, increased from 65.6 to 96.1 mg lignin g −1 in needles and 35.3–83.6 mg lignin g −1 in litters, which followed a trend of increasing soil base saturation under P. sylvestris stands. The concentration of NaOH-extractable moieties in needles increased from 1.79 to 2.35 μg sample g −1 with soil base saturation, as did the acid to aldehyde ratios of phenylpropanoid moieties in NaOH-extracts from litters. We conclude that the quality of lignin in needles and litter, as measured by its phenylpropanoid characteristics, varied significantly in P. sylvestris stands. In the light of the evidence from other studies that phenylpropanoid moieties have significantly different rates of microbial decomposition, this aspect of lignin quality should be considered when modelling the rate of litter mass loss and organic matter accumulation in forest soils. Furthermore, we have shown that by combining the CuO-oxidation technique with a NaOH-extraction procedure, phenylpropanoid signatures of a ‘bound’ and a relatively ‘labile’ lignin derived fraction in needles and litters can be more accurately monitored. A more extensive study is required to clarify the apparent relationships between the soil chemical characteristics beneath stands and the quality of lignin in plant materials.

Fate of triclosan in field soils receiving sewage sludge.

The anti-microbial substance triclosan can partition to sewage sludge during wastewater treatment and subsequently transfer to soil when applied to land. Here, we describe the fate of triclosan in a one-year plot experiment on three different soils receiving sludge. Triclosan and methyl-triclosan concentrations were measured in soil samples collected monthly from three depths. A large fraction of triclosan loss appeared to be explained by transformation to methyl-triclosan. After 12 months less than 20% of the initial triclosan was recovered from each soil. However, the majority was recovered as methyl-triclosan. Most of the chemical recovered at the end of the experiment (both triclosan and methyl-triclosan) was still in the top 10 cm layer, although there was translocation to lower soil horizons in all three soils. Between 16.5 and 50.6% of the applied triclosan was unaccounted for after 12 months either as a consequence of degradation or the formation of non-extractable residues.

Modeling the fate of down-the-drain chemicals in rivers: An improved software for GREAT-ER

Abstract GREAT-ER (Geography-referenced Regional Exposure Assessment Tool for European Rivers) is a model system for predicting chemical fate and exposure in surface waters. The GREAT-ER approach combines a series of well-studied models (for sewers, waste water treatment plants and rivers) with spatial information managed by a GIS. A new version of GREAT-ER (version 2) has been developed which has a number of improved features compared to its predecessor. All components are now implemented as Free Software and make use of Free Software where possible. This simplifies the distribution, use and extension of the system and its components for scientific applications. In addition, two new platform-independent user interfaces have been developed. The first is a simplified web-based interface for easy access without installation and the second is a full-featured desktop version. The model system has been re-designed to increase its flexibility for the modification and extension of its component models. In addition, the file-based data storage system used in version 1 has been replaced by a database management system with a flexible Application Programming Interface (API). This makes it easier for users to share their results, using a new repository (also with web-based and desktop versions) serving as a central communication tool. The output from the new system has been successfully tested against the field-validated models in GREAT-ER 1.0.

A simple stochastic model of point source solute transport in rivers based on gauging station data with implications for sampling requirements

A simple point-source water quality model was constructed to explore hypothetical scenarios of linear alkylbenzene sulphonate (LAS) load variability, chemical degradation kinetics, river discharge and river velocities within the context of planned water quality monitoring in the river Lambro, northern Italy. LAS is an anionic surfactant and a commonly used ingredient of household detergents. Input loads were derived from flow and concentration measurements at sewage treatment works (STW). River travel times are approximated using hydraulic geometry concepts based on existing records of stage, discharge and velocity measurements. The model proved to be especially useful in predicting the impact of overflows from an undersized STW near the top of the catchment on diurnal variations in water quality downstream. Probability density functions (pdfs) of LAS concentrations for a number of points on the river were approximated by running the model stochastically (using a Monte Carlo procedure) over independent frequency distributions of discharge, temperature and input load. The predicted concentration pdfs were then used to estimate the number of random grab and 24 h composite samples, which would be required in order to estimate mean concentrations with confidence. This is especially important in situations where the analysis is expensive and the sample budget is limited. The model results showed that grab sampling was not a viable strategy in the Lambro largely due to the very strong diurnal variability in concentrations induced by the STW overflow. This conclusion was corroborated by field data.