Karina Yew-Hoong Gin

Impacts of emerging organic contaminants on freshwater resources: Review of recent occurrences, sources, fate and effects

Rapid urbanization and frequent disposal of wastewater to surface water cause widespread contamination of freshwater supplies with emerging contaminants, such as pharmaceuticals, insecticides, surfactants, endocrine disruptors, including hormones. Although these organic contaminants may be present at trace levels, their adverse effects on aquatic life, animals and even humans are a growing concern. Numerous studies have been published on the occurrence and fate of emerging organic contaminants in different parts of the world, spanning a wide range of sources and aquatic environments including freshwater catchments, effluent wastewater streams, lakes, rivers, reservoirs, estuaries and marine waters. This paper reviews recent studies on the occurrence and fate of frequently detected pharmaceuticals and hormones and identifies areas that merit further research.

Emerging contaminants of public health significance as water quality indicator compounds in the urban water cycle.

The contamination of the urban water cycle (UWC) with a wide array of emerging organic compounds (EOCs) increases with urbanization and population density. To produce drinking water from the UWC requires close examination of their sources, occurrence, pathways, and health effects and the efficacy of wastewater treatment and natural attenuation processes that may occur in surface water bodies and groundwater. This paper researches in details the structure of the UWC and investigates the routes by which the water cycle is increasingly contaminated with compounds generated from various anthropogenic activities. Along with a thorough survey of chemicals representing compound classes such as hormones, antibiotics, surfactants, endocrine disruptors, human and veterinary pharmaceuticals, X-ray contrast media, pesticides and metabolites, disinfection-by-products, algal toxins and taste-and-odor compounds, this paper provides a comprehensive and holistic review of the occurrence, fate, transport and potential health impact of the emerging organic contaminants of the UWC. This study also illustrates the widespread distribution of the emerging organic contaminants in the different aortas of the ecosystem and focuses on future research needs.

Novel perspectives on the bioaccumulation of PFCs--the concentration dependency.

The effects of exposure concentration on the bioaccumulation of four perfluorinated chemicals (PFCs): perfluorooctanesulfonate (PFOS), perfluoroocanoic acid (PFOA), perfluorononanoic acid (PFNA), and perfluorodecanoic acid (PFDA), was investigated using green mussels, Perna viridis. Mussels were exposed to concentrations of 1 μgL(-1) and 10 μgL(-1) of each PFC for 56 days, and the bioaccumulation factors (BAF) were found to range from 15 to 859 L/kg and from 12 to 473 L/kg at 1 μgL(-1) and 10 μgL(-1), respectively. For all compounds, the BAF was larger at the lower dosage. Results suggest that the bioaccumulation of PFCs is concentration dependent. This concentration dependency can be explained by a nonlinear adsorption mechanism, which was further supported by the experimental results. The sensitivity of BAF to exposure concentration was found to be positively related to perfluorinated chain length and the binding affinity of the compounds. Bioaccumulation of long chain carboxylates and sulfonates are more easily affected by concentration changes. The validity of the conventional kinetic method was examined by comparing the results with the fundamental steady-state method: in addition to the above-mentioned batch test, mussels were also subject to 24-day exposure (1 μgL(-1) and 10 μgL(-1)) followed by 24-day depuration. Contradictions were found in the resulting kinetic BAF and model curving fittings. A new kinetic model based on adsorption mechanism was proposed, which potentially provide more accurate description of the bioaccumulation process of PFCs.

Derivation and application of a new model for heavy metal biosorption by algae

An equilibrium model for describing the relationships between important parameters for heavy metal sorption by algae was derived through a thermodynamics approach. In this model, both the removal efficiency of heavy metal and metal adsorption per unit algal biomass are considered to be simple functions of the ratio of algal biomass concentration to the initial metal concentration for selected conditions, i.e. as at constant pH and temperature. The model was found to fit the experimental results well (judged by the correlation-regression coefficient, R2), for the adsorption of cadmium, copper, lead and zinc by two algal species, Oocystis sp. (both living and non-living) and Chlorococcum sp. The applicability of the model was also supported by the reprocessed results of experimental data given in the literature, i.e. for the metal species, Cd, Pb, Cu and Ag, the algal species, Chlorella vulgaris, Scenedesmus quadricauda and Cladophora crispata, and both batch and continuous fixed-bed reactors. It was also demonstrated that the model could be applied over a broad range of pH for cadmium and copper adsorption by Oocystis sp. However, the model was not applicable at very low and high pH levels, due to negligible adsorption and precipitation, respectively.

A multiphase oil spill model

A multiphase oil spill model has been developed to simulate consequences of accidental oil spills in the marine environment. Six state variables are computed simultaneously: an oil slick thickness on the water surface; concentration of dissolved, emulsified and paniculate oil phases in the water column; and concentration of dissolved and paniculate oil phases in the bottom sediments. A consistent Eulerian approach is applied across the model, the oil slick thickness is computed using the layer-averaged Navier-Stokes equations, and for transport of the oil phases in the water column the advection-diffusion equation is employed. The kinetic terms are developed to control the oil mass exchange between the variables. The governing equations are verified using test cases, data and other models. The model is useful for short and long-term predictions of the spilled oil dynamics and fate, including application of the oil combating elements, such as chemical dispersants and booms.

Occurrence of emerging organic contaminants in a tropical urban catchment in Singapore

Emerging organic contaminants (EOCs) occurring in urban runoff can negatively impact sensitive ecosystems and drinking water resources. The occurrence of 13 EOCs was characterized in the Marina Catchment, a large urban catchment approximately one-sixth the area of Singapore. The 13 EOCs included alkylphenol ethoxylate metabolites (APEMs), hormones, pharmaceuticals, bisphenol A, and a pesticide (fipronil). The APEMs were most prevalent with concentrations of nonylphenol ethoxyacetic acid (NP1EC) and nonlyphenol (NP) ranging from several ng L(-1) to 6 μg L(-1) and 4 μg L(-1), respectively, while concentrations of octylphenol ethoxyacetic acid (OP1EC), dicarboxylated alkylphenol ethoxyacetic acid (CA3P1EC, CA4P1EC) were as high as 0.9 μg L(-1). Other EOCs were present in the ng L(-1) range: chloramphenicol 1-15 ng L(-1), ibuprofen 2-76 ng L(-1), naproxen 8-108 ng L(-1), bisphenol A 30-625 ng L(-1), fipronil 1-72 ng L(-1), estrone 1-304 ng L(-1), estriol 3-451 ng L(-1). The APEMs and EOCs detected appear to enter canals and rivers from non-point sources, possibly from runoff and leaking sewer lines. The closure of Marina Bay with a barrage has resulted in significantly higher levels of APEMS compared to when the bay was open to the sea. Depth profiles show that NP1EC and OP1EC were notably lower in deep waters compared to surface waters. NP, estrone and estriol exceeded literature-based Predicted No Effect Concentration (PNEC) values.

An Oil Spill–Food Chain Interaction Model for Coastal Waters

An oil spill-food chain interaction model, composed of a multiphase oil spill model (MOSM) and a food chain model, has been developed to assess the probable impacts of oil spills on several key marine organisms (phytoplankton, zooplankton, small fish, large fish and benthic invertebrates). The MOSM predicts oil slick thickness on the water surface; dissolved, emulsified and particulate oil concentrations in the water column; and dissolved and particulate oil concentrations in bed sediments. This model is used to predict the fate of oil spills and transport with respect to specific organic compounds, while the food chain model addresses the uptake of toxicant by marine organisms. The oil spill-food chain interaction model can be used to assess the environmental impacts of oil spills in marine ecosystems. The model is applied to the recent Evoikos-Orapin Global oil spill that occurred in the Singapore Strait.

Fecal pollution source tracking toolbox for identification, evaluation and characterization of fecal contamination in receiving urban surface waters and groundwater

The quality of surface waters/groundwater of a geographical region can be affected by anthropogenic activities, land use patterns and fecal pollution sources from humans and animals. Therefore, the development of an efficient fecal pollution source tracking toolbox for identifying the origin of the fecal pollution sources in surface waters/groundwater is especially helpful for improving management efforts and remediation actions of water resources in a more cost-effective and efficient manner. This review summarizes the updated knowledge on the use of fecal pollution source tracking markers for detecting, evaluating and characterizing fecal pollution sources in receiving surface waters and groundwater. The suitability of using chemical markers (i.e. fecal sterols, fluorescent whitening agents, pharmaceuticals and personal care products, and artificial sweeteners) and/or microbial markers (e.g. F+RNA coliphages, enteric viruses, and host-specific anaerobic bacterial 16S rDNA genetic markers) for tracking fecal pollution sources in receiving water bodies is discussed. In addition, this review also provides a comprehensive approach, which is based on the detection ratios (DR), detection frequencies (DF), and fate of potential microbial and chemical markers. DR and DF are considered as the key criteria for selecting appropriate markers for identifying and evaluating the impacts of fecal contamination in surface waters/groundwater.

Alternative Fecal Indicators and Their Empirical Relationships with Enteric Viruses, Salmonella enterica, and Pseudomonas aeruginosa in Surface Waters of a Tropical Urban Catchment

ABSTRACT The suitability of traditional microbial indicators (i.e., Escherichia coli and enterococci) has been challenged due to the lack of correlation with pathogens and evidence of possible regrowth in the natural environment. In this study, the relationships between alternative microbial indicators of potential human fecal contamination (Bacteroides thetaiotaomicron, Methanobrevibacter smithii, human polyomaviruses [HPyVs], and F+ and somatic coliphages) and pathogens (Salmonella spp., Pseudomonas aeruginosa, rotavirus, astrovirus, norovirus GI, norovirus GII, and adenovirus) were compared with those of traditional microbial indicators, as well as environmental parameters (temperature, conductivity, salinity, pH, dissolved oxygen, total organic carbon, total suspended solids, turbidity, total nitrogen, and total phosphorus). Water samples were collected from surface waters of urban catchments in Singapore. Salmonella and P. aeruginosa had significant positive correlations with most of the microbial indicators, especially E. coli and enterococci. Norovirus GII showed moderately strong positive correlations with most of the microbial indicators, except for HPyVs and coliphages. In general, high geometric means and significant correlations between human-specific markers and pathogens suggest the possibility of sewage contamination in some areas. The simultaneous detection of human-specific markers (i.e., B. thetaiotaomicron, M. smithii, and HPyVs) with E. coli and enterococcus supports the likelihood of recent fecal contamination, since the human-specific markers are unable to regrow in natural surface waters. Multiple-linear-regression results further confirm that the inclusion of M. smithii and HPyVs, together with traditional indicators, would better predict the occurrence of pathogens. Further study is needed to determine the applicability of such models to different geographical locations and environmental conditions.

Investigation of pharmaceuticals, personal care products and endocrine disrupting chemicals in a tropical urban catchment and the influence of environmental factors.

Previous studies showed the presence of multiple emerging organic contaminants (EOCs) in urban surface waters of Singapore even though there are no obvious direct wastewater discharges. In this study, we investigated the occurrence and distribution of 17 pharmaceuticals and personal care products (PPCPs) and endocrine disruptive compounds (EDCs) in a tropical urban catchment of Singapore. Monthly samples were collected from a reservoir and its 5 upstream tributaries during a 16-month period. Analysis of samples showed all sites had measurable PPCP and EDC concentrations, with caffeine (33.9-2980 ng/L), salicylic acid (5-838 ng/L), acetaminophen (<4-485.5 ng/L), BPA (<2-919.5 ng/L) and DEET (13-270 ng/L) being the most abundant. Marked differences in concentrations of target analytes between the reservoir and upstream tributaries were observed, and were tentatively attributed to the spatial differences in source inputs, water dilution capacity as well as natural attenuation of EOCs. Significant correlations between EOCs and conductivity, dissolved oxygen, chlorophyll a, turbidity, nutrients and cumulative precipitation were observed. These factors appeared to affect the distribution and attenuation of EOCs, depending on their physicochemical properties. Rainfall also influenced the temporal distribution of caffeine, BPA, triclosan, fipronil and DEET in the reservoir. Ecological risk assessment showed that caffeine, acetaminophen, estrone, BPA, triclosan and fipronil may warrant further survey. In particular, BPA levels exceeded the literature-based Predicted No-Effect Concentration (PNEC) value, highlighting the need for source control and/or water remediation in this urban catchment.