Coastal water quality impact of stormwater runoff from an urban watershed in southern California

Field studies were conducted to assess the coastal water quality impact of stormwater runoff from the Santa Ana River, which drains a large urban watershed located in southern California. Stormwater runoff from the river leads to very poor surf zone water quality, with fecal indicator bacteria concentrations exceeding California ocean bathing water standards by up to 500%. However, cross-shore currents (e.g., rip cells) dilute contaminated surf zone water with cleaner water from offshore, such that surf zone contamination is generally confined to < 5 km around the river outlet. Offshore of the surf zone, stormwater runoff ejected from the mouth of the river spreads out over a very large area, in some cases exceeding 100 km2 on the basis of satellite observations. Fecal indicator bacteria concentrations in these large stormwater plumes generally do not exceed California ocean bathing water standards, even in cases where offshore samples test positive for human pathogenic viruses (human adenoviruses and enteroviruses) and fecal indicator viruses (F+ coliphage). Multiple lines of evidence indicate that bacteria and viruses in the offshore stormwater plumes are either associated with relatively small particles (< 53 microm) or not particle-associated. Collectively, these results demonstrate that stormwater runoff from the Santa Ana River negatively impacts coastal water quality, both in the surf zone and offshore. However, the extent of this impact, and its human health significance, is influenced by numerous factors, including prevailing ocean currents, within-plume processing of particles and pathogens, and the timing, magnitude, and nature of runoff discharged from river outlets over the course of a storm.     

Use of fecal steroids to infer the sources of fecal indicator bacteria in the Lower Santa Ana River Watershed, California: sewage is unlikely a significant source

The Santa Ana River (SAR), CA and adjacent wetlands have been identified as potential sources of fecal indicator bacteria (FIB) to the surf zone at Huntington Beach, CA. A suite of fecal steroids, including coprostanol (COP), epicoprostanol (eCOP), cholesterol (CHOE), cholestanol (CHOA), alpha-cholestanone (aONE), beta-cholestanone (bONE), beta-sitosterol (bSIT), stigmasterol (STIG), stigmastanol (STAN), and campesterol (CAM), were used as chemical markers to examine whether sewage was a significant source of FIB within the lower Santa Ana River watershed. A total of 54 water samples were collected from three locations in the intertidal zone near the mouth of the Santa Ana River at different tidal stages. Steroid ratios in SAR samples were different from those found in raw and treated sewage from a local wastewater treatment plant or in nearby effluent plume and did not appear to be influenced by the sampling location, daily tides, and spring/neap tidal cycle. The characteristics of steroid ratios suggested a diagenetic ratherthan a biogenic source forthe COP content of the samples. The log-based concentrations of COP and FIB in the SAR samples were not significantly correlated, inconsistent with sewage being the source of FIB in the study area. In addition, multivariate statistical analysis showed that the concentrations of FIB were better correlated with bird fecal steroids than with the typical sewage sterols. The results implied that sewage was not a significant source of fecal steroids, and therefore perhaps FIB to the study area. Instead, birds may be one possible source of the intermittently high levels of FIB observed in the lower Santa Ana River watershed and the nearby surf zone.     

Flow fingerprinting fecal pollution and suspended solids in stormwater runoff from an urban coastal watershed

Field studies were conducted to characterize the concentration vs streamflow relationships (or "flow fingerprints") of fecal pollution and suspended solids in stormwater runoff from the Santa Ana River watershed, the largest watershed in southern California. The concentrations of fecal indicator bacteria and F+ coliphages (viruses infecting E. coli) exhibit little-to-no dependence on streamflow rates, whereas the concentrations of total suspended solids (TSS) exhibit a very strong (power-law) dependence on streamflow rates. The different flow fingerprints observed for fecal pollutants, on one hand, and TSS, on the other hand, reflect different sources and transport pathways for these stormwater constituents. The flow-independent nature of fecal indicator bacteria and F+ coliphages is consistent with the idea that these contaminants are ubiquitously present on the surface of the urban landscape and rapidly partition into the surface water as the landscape is wetted by rainfall. The flow-dependent nature of TSS, on the other hand, is usually ascribed to the shear-induced erosion of channel bed sediments and/or the expansion of drainage area contributing to runoff. The apparent ubiquity of fecal indicator bacteria and F+ coliphages, together with the very high storm-loading rates of fecal indicator bacteria and the low detection frequency of human adenovirus and human enterovirus, suggest that fecal pollution in stormwater runoff from the Santa Ana River watershed is primarily of nonhuman waste origin.     

Decadal and shorter period variability of surf zone water quality at Huntington Beach,California

The concentration of fecal indicator bacteria in the surf zone at Huntington Beach, CA, varies over time scales that span at least 7 orders of magnitude, from minutes to decades. Sources of this variability include historical changes in the treatment and disposal of wastewater and dry weather runoff, El Ni?o events, seasonal variations in rainfall, spring-neap tidal cycles, sunlight-induced mortality of bacteria, and nearshore mixing. On average, total coliform concentrations have decreased over the past 43 years, although point sources of shoreline contamination (storm drains, river outlets, and submarine outfalls) continue to cause transiently poor water quality. These transient point sources typically persist for 5-8 yr and are modulated by the phase of the moon, reflecting the influence of tides on the sourcing and transport of pollutants in the coastal ocean. Indicator bacteria are very sensitive to sunlight therefore, the time of day when samples are collected can influence the outcome of water quality testing. These results demonstrate that coastal water quality is forced by a complex combination of local and external processes and raise questions about the efficacy of existing marine bathing water monitoring and reporting programs.     

Scaling and management of fecal indicator bacteria in runoff from a coastal urban watershed in southern California

This paper describes a series of field studies aimed at identifying the spatial distribution and flow forcing of fecal indicator bacteria in dry and wet weather runoff from the Talbert watershed, a highly urbanized coastal watershed in southern California. Runoff from this watershed drains through tidal channels to a popular public beach, Huntington State Beach, which has experienced chronic surf zone water quality problems over the past several years. During dry weather, concentrations of fecal indicator bacteria are highest in inland urban runoff, intermediate in tidal channels harboring variable mixtures of urban runoff and ocean water, and lowest in ocean water at the base of the watershed. This inland-to-coastal gradient is consistent with the hypothesis that urban runoff from the watershed contributes to coastal pollution. On a year round basis, the vast majority (>99%) of fecal indicator bacteria loading occurs during storm events when runoff diversions, the management approach of choice, are not operating. During storms, the load of fecal indicator bacteria in runoff follows a power law of the form L approximately Qn, where L is the loading rate (in units of fecal indicator bacteria per time), Q is the volumetric flow rate (in units of volume per time), and the exponent n ranges from 1 to 1.5. This power law and the observed range of exponent values are consistent with the predictions of a mathematical model that assumes fecal indicator bacteria in storm runoff originate from the erosion of contaminated sediments in drainage channels or storm sewers. The theoretical analysis, which is based on a conventional model for the shear-induced erosion of particles from land and channel-bed surfaces, predicts that the magnitude of the exponent n reflects the geometry of the stormwater conveyance system from which the pollution derives. This raises the possibility that the scaling properties of pollutants in stormwater runoff (i.e., the value of n) may harbor information about the origin of nonpoint source pollution.     

Treatment of dry weather urban runoff in tidal saltwater marshes: A longitudinal study of the Talbert Marsh in southern California

The scientific literature presents conflicting assessments of whether tidal saltwater wetlands reduce or increase fecal indicator bacteria (FIB) impairment of marine bathing waters. In this paper we describe the use of a two end-member salinity-mixing model to calculate FIB treatment efficiencies for the Talbert Marsh, a tidal saltwater wetland in Orange County, California. The mixing model utilized FIB and salinity measurements (n = 10 716) collected during a three-year longitudinal study of the Talbert Marsh. Over the course of the study the marsh received progressively less dry weather surface water runoff from the surrounding urban landscape due to the implementation of a runoff interception and treatment program. As the volume of dry-weather runoff entering the marsh declined, the Talbert Marsh more efficiently removed one FIB group (total coliform) and became a significantly smaller source of two other FIB groups (Escherichia coli and enterococci bacteria). Hence, there may be a maximum volume of dry weather urban runoff (in this case < 1% of the average tidal prism of 2.35 x 10(5) m3/day) that a tidal saltwater wetland can receive, above which the wetland is a net source of FIB to coastal waters.     

Model of microbial transport and inactivation in the surf zone and application to field measurements of total coliform in Northern Orange County, California

The classic model of pollutant transport in the surf zone of a long, sandy beach developed by Inman et al. (J. Geophys. Res. 1971, 76, 3493) is altered to account for first-order pollutant inactivation in an effort to understand how rip cell dilution and bacterial inactivation control the length of shoreline adversely impacted by microbial pollution from a point source. A dimensionless number gamma dictates whether physical processes (dilution of microbes in the surf zone by rip cell mixing) or biological processes (microbial inactivation) control the distribution of pollution along the shoreline. Estimates of gamma for beaches in Northern Orange County, California, indicate that dilution is the primary factor controlling total coliform levels surrounding two drains that release nuisance runoff directly onto the beach. It is also shown that, even when alongshore currents are fast, pollutant levels will drop e-fold at distances under 4000 m from the point source due to dilution alone. Because dilution is ultimately controlled by wave climate and shoreline morphology, the results suggest the strategic position of drains and other point sources in high dilution wave environments will reduce potential adverse effects on beach water quality. In addition, the results stress the importance of understanding hydrodynamics when conducting microbial source tracking at wave-dominated marine beaches.     

Beach boundary layer: a framework for addressing recreational water quality impairment at enclosed beaches

Nearshore waters in bays, harbors, and estuaries are frequently contaminated with human pathogens and fecal indicator bacteria. Tracking down and mitigating this contamination is complicated by the many point and nonpoint sources of fecal pollution that can degrade water quality along the shore. From a survey of the published literature, we propose a conceptual and mathematical framework, the "beach boundary layer model", for understanding and quantifying the relative impact of beach-side and bay-side sources of fecal pollution on nearshore water quality. In the model, bacterial concentration in ankle depth water C(ankle) [bacteria L(-3)] depends on the flux m' [bacteria L(-2) T(-1)] of fecal bacteria from beach-side sources (bather shedding, bird and dog feces, tidal washing of sediments, decaying vegetation, runoff from small drains, and shallow groundwater discharge), a cross-shore mass transfer velocity k [L T(-1)] that accounts for the physics of nearshore transport and mixing, and a background concentration C(bay) [bacteria L(-3)] attributable to bay-side sources of pollution that impact water quality over large regions (sewage outfalls, creeks and rivers): C(ankle) = m'/k + C(bay). We demonstrate the utility of the model for identifying risk factors and pollution sources likely to impact shoreline water quality, and evaluate the model's underlying assumptions using computational fluid dynamic simulations of flow, turbulence, and mass transport in a trapezoidal channel.     

Anthropogenic currents and shoreline water quality in Avalon Bay, California

Shoreline concentrations of fecal indicator bacteria (FIB) and fecal indicator viruses (FIV) in Avalon Bay (Catalina Island, California) display a marked diurnal pattern (higher at night and lower during the day) previously attributed to the tidal flux of sewage-contaminated groundwater and the tidal washing of contaminated sediments, coupled with light and dark die-off of FIB and FIV (Boehm, et al., Environ. Sci. Technol. 2009, 43, 8046-8052). In this paper we document the existence of strong (peak velocities between 20 to 40 cm/s) transient currents in the nearshore waters of Avalon Bay that occur between 07:00 and 20:00 each day. These currents, which have a significant onshore component, are generated by anthropogenic activities in the Bay, including prop wash from local boat traffic and the docking practices of large passenger ferries. A budget analysis carried out on simultaneous measurements of FIB at two cross-shore locations indicates that anthropogenic currents contribute to the diurnal cycling of FIB concentrations along the shoreline, by transporting relatively unpolluted water from offshore toward the beach. The data and analysis presented in this paper support the idea that anthropogenic currents represent a significant, and previously overlooked, source of variability in shoreline water quality.     

Groundwater discharge: potential association with fecal indicator bacteria in the surf zone

Short-lived radium isotopes (223Ra and 224Ra) are used to investigate the potential association between groundwater discharge and microbial pollution at Huntington Beach, CA. We establish the tidally driven exchange of groundwater from the surficial beach aquifer across the beach face. Groundwater is found to be a source of nutrients (silica, inorganic nitrogen, and orthophosphate) to the surf zone, and these nutrients could possibly provide an environment for enhanced growth or increased persistence of fecal indicator bacteria (FIB). Ammonium and ortho-phosphate explain up to 12-20% of the variance in FIB levels in the surf zone. Elevated levels of FIB were only found in 1 of the 26 groundwater samples. However, FIB in the surf zone covary with radium at fortnightly, diurnal, and semi-diurnal tidal periods. In addition, radium accounts for up to 38% of the variance in log-FIB levels in the surf zone. A column experiment illustrates that Enterococcus suspended in Huntington Beach saline groundwater is not significantly filtered by sand collected from the field. This work establishes a mechanism for the subterranean delivery of FIB pollution to the surf zone from the surficial aquifer and presents evidence that supports an association between groundwater discharge and FIB.     

Tiered approach for identification of a human fecal pollution source at a recreational beach: case study at Avalon Bay,Catalina Island,California

Recreational marine beaches in California are posted as unfit for swimming when the concentration of fecal indicator bacteria (FIB) exceeds any of seven concentration standards. Finding and mitigating sources of shoreline FIB is complicated by the many potential human and nonhuman sources of these organisms and the complex fate and transport processes that control their concentrations. In this study, a three-tiered approach is used to identify human and nonhuman sources of FIB in Avalon Bay, a popular resort community on Catalina Island in southern California. The first and second tiers utilize standard FIB tests to spatially isolate the FIB signal, to characterize the variability of FIB over a range of temporal scales, and to measure FIB concentrations in potential sources of these organisms. In the third tier, water samples from FIB "hot spots" and sources are tested for human-specific bacteria Bacteroides/Prevotella and enterovirus to determine whether the FIB are from human sewage or from nonhuman sources such as bird feces. FIB in Avalon Bay appear to be from multiple, primarily land-based, sources including bird droppings, contaminated subsurface water, leaking drains, and runoff from street wash-down actvities. Multiple shoreline samples and two subsurface water samples tested positive for human-specific bacteria and enterovirus, suggesting that at least a portion of the FIB contamination is from human sewage.     

Identifying pollutant sources in tidally mixed systems: case study of fecal indicator bacteria from marinas in Newport Bay, southern California

This study investigates the contribution of several marinas to fecal indicator bacteria impairment in Newport Bay, a regionally important tidal embayment in southern California. Three different fecal indicator bacteria groups were assayed, including total coliform, Escherichia coli, and enterococci bacteria, all measured using the IDEXX Colilert and Enterolert system. To document temporal variability in the fecal indicator bacteria signal, water column samples (n = 4132) were collected from two marinas over time scales ranging from hours to months. To document spatial variability of the fecal indicator bacteria signal, water column and sediment samples were collected from a number of sites (n = 11 to 36, depending on the study) in and around the two marinas, over spatial scales ranging from meters to kilometers. To identify the dominant temporal and spatial patterns in these data a statistical approach--Empirical Orthogonal Function analysis--was utilized. Finally, to clarify the transport pathways responsible for the observed temporal and spatial patterns, fecal indicator bacteria data were compared to simultaneous measurements of tidal flow, temperature, and salinity. The results of this field effort collectively implicate runoff--both dry weather runoff at sampling sites located near some storm drains and wet weather runoff at all sites--as a primary source of fecal indicator bacteria in the water column and subtidal sediments. The results and analysis presented here reinforce the growing body of evidence that management of fecal indicator bacteria impairment in the coastal waters of southern California will require developing long-term strategies for treating nonpoint sources of both dry weather and stormwater runoff.     

Wave-induced mass transport affects daily Escherichia coli fluctuations in nearshore water

Characterization of diel variability of fecal indicator bacteria concentration in nearshore waters is of particular importance for development of water sampling standards and protection of public health. Significant nighttime increase in Escherichia coli (E. coli) concentration in beach water, previously observed at marine sites, has also been identified in summer 2000 from fixed locations in waist- and knee-deep waters at Chicago 63rd Street Beach, an embayed, tideless, freshwater beach with low currents at night (approximately 0.015 m s(-1)). A theoretical model using wave-induced mass transport velocity for advection was developed to assess the contribution of surface waves to the observed nighttime E. coli replenishment in the nearshore water. Using average wave conditions for the summer season of year 2000, the model predicted an amount of E. coli transported from water of intermediate depth, where sediment resuspension occurred intermittently, that would be sufficient to have elevated E. coli concentration in the surf and swash zones as observed. The nighttime replenishment of E. coli in the surf and swash zones revealed here is an important phase in the cycle of diel variations of E. coli concentration in nearshore water. According to previous findings in Ge et al. (Environ. Sci. Technol. 2010, 44, 6731-6737), enhanced current circulation in the embayment during the day tends to displace and deposit material offshore, which partially sets up the system by the early evening for a new period of nighttime onshore movement. This wave-induced mass transport effect, although facilitating a significant base supply of material shoreward, can be perturbed or significantly influenced by high currents (orders of magnitude larger than a typical wave-induced mass transport velocity), current-induced turbulence, and tidal forcing.     

Influence of climate change, tidal mixing, and watershed urbanization on historical water quality in Newport Bay, a saltwater wetland and tidal embayment in southern California

Historical coliform measurements (n = 67,269; 32 years) in Newport Bay, a regionally important saltwater wetland and tidal embayment in southern California, have been compiled and analyzed. Coliform concentrations in Newport Bay decrease along an inland-to-ocean gradient, consistent with the hypothesis that this tidal embayment attenuates fecal pollution from inland sources. Nearly 70% of the variability in the coliform record can be attributed to seasonal and interannual variability in local rainfall, implying that stormwater runoff from the surrounding watershed is a primary source of coliform in Newport Bay. The storm loading rate of coliform from the San Diego Creek watershed--the largest watershed draining into Newport Bay--appears to be unaffected by the dramatic shift away from agricultural land-use that occurred in the watershed over the study period. Further, the peak loading of coliform during storms is larger than can be reasonably attributed to sources of human sewage, suggesting that nonhuman fecal pollution and/or bacterial regrowth contribute to the coliform load. Summer time measurements of coliform exhibit interannual trends, but these trends are site specific, apparently due to within-Bay variability in land-use, inputs of dry-weather runoff, and tidal mixing rates. Overall, these results suggest that efforts to improve water quality in Newport Bay will likely have greater efficacy during dry weather summer periods. Water quality during winter storms, on the other hand, appears to be dominated by factors outside of local management control; namely, virtually unlimited nonhuman sources of coliform in the watershed and global climate patterns, such as the El Nino Southern Oscillation, that modulate rainfall and stormwater runoff in southern California.     

Application of phylogenetic microarray analysis to discriminate sources of fecal pollution

Conventional methods for fecal source tracking typically use single biomarkers to systematically identify or exclude sources. High-throughput DNA sequence analysis can potentially identify all sources of microbial contaminants in a single test by measuring the total diversity of fecal microbial communities. In this study, we used phylogenetic microarray analysis to determine the comprehensive suite of bacteria that define major sources of fecal contamination in coastal California. Fecal wastes were collected from 42 different populations of humans, birds, cows, horses, elk, and pinnipeds. We characterized bacterial community composition using a DNA microarray that probes for 16S rRNA genes of 59,316 different bacterial taxa. Cluster analysis revealed strong differences in community composition among fecal wastes from human, birds, pinnipeds, and grazers. Actinobacteria, Bacilli, and many Gammaproteobacteria taxa discriminated birds from mammalian sources. Diverse families within the Clostridia and Bacteroidetes taxa discriminated human wastes, grazers, and pinnipeds from each other. We found 1058 different bacterial taxa that were unique to either human, grazing mammal, or bird fecal wastes. These OTUs can serve as specific identifier taxa for these sources in environmental waters. Two field tests in marine waters demonstrate the capacity of phylogenetic microarray analysis to track multiple sources with one test.     

Black carbon from the Mississippi River: quantities,sources, and potential implications for the global carbon cycle

Black carbon (BC) may be a major component of riverine carbon exported to the ocean, but its flux from large rivers is unknown. Furthermore, the global distribution of BC between natural and anthropogenic sources remains uncertain. We have determined BC concentrations in suspended sediments of the Mississippi River, the 7th largest river in the world in terms of sediment and water discharge, during high flow and low flow in 1999. The 1999 annual flux of BC from the Mississippi River was 5 x 10(-4) petagrams (1 Pg = 10(15) g = 1 gigaton). We also applied a principal components analysis to particulate-phase high molecular weight polycyclic aromatic hydrocarbon isomer ratios in Mississippi River suspended sediments. In doing so, we determined that approximately 27% of the BC discharged from the Mississippi River in 1999 originated from fossil fuel combustion (coal and smelter-derived combustion), implicating fluvial BC as an important source of anthropogenic BC contamination into the ocean. Using our value for BC flux and the annual estimate for BC burial in ocean sediments, we calculate that, in 1999, the Mississippi River discharged approximately 5% of the BC buried annually in the ocean. These results have important implications, not only for the global carbon cycle but also for the fluvial discharge of particulate organic contaminants into the world's oceans.     

Public mis-notification of coastal water quality: a probabilistic evaluation of posting errors at Huntington Beach, California

Whenever measurements of fecal pollution in coastal bathing waters reach levels that might pose a significant health risk, warning signs are posted on public beaches in California. Analysis of historical shoreline monitoring data from Huntington Beach, southern California, reveals that protocols used to decide whether to post a sign are prone to error. Errors in public notification (referred to here as posting errors) originate from the variable character of pollutant concentrations in the ocean, the relatively infrequent sampling schedule adopted by most monitoring programs (daily to weekly), and the intrinsic error associated with binary advisories in which the public is either warned or not. In this paper, we derive a probabilistic framework for estimating posting error rates, which at Huntington Beach range from 0 to 41%, and show that relatively high sample-to-sample correlations (>0.4) are required to significantly reduce binary advisory posting errors. Public mis-notification of coastal water quality can be reduced by utilizing probabilistic approaches for predicting current coastal water quality, and adopting analog, instead of binary, warning systems.     

On-farm and postharvest processing sources of bacterial contamination to melon rinds

Multistate and international foodborne illness outbreaks, particularly involving cantaloupe and often involving rare Salmonella spp., have increased dramatically over the past 13 years. This study assessed the sources and extent of melon rind contamination in production fields and at processing and packing facilities. In the spring of 1999, cantaloupe (Cucumis melo L. [reticulatus group] cv. Cruiser) sampled from two sites in the Rio Grande River Valley showed that postharvest-processed melon rinds often had greater plate counts of bacterial contaminants than field-fresh melons. Cantaloupe in the field had 2.5 to 3.5 log CFU g(-1) rind total coliforms by aerobic plate counts, whereas washed melons had 4.0 to 5.0 log CFU g(-1). In the fall of 1999, coliforms on honeydew melons (C. melo [inodorous group] cv. Honey Brew) ranged from 2.6 to 3.7 log CFU g(-1) after processing, and total and fecal coliforms and enterococci never fell below 2.5 log CFU g(-1). A hydrocooler at another site contaminated cantaloupe rinds with up to 3.4 log CFU g(-1) total and fecal enterococci; a secondary rinse with chlorinated water incompletely removed these bacteria. Sources of coliforms and enterococci were at high levels in melon production soils, especially in furrows that were flood irrigated, in standing water at one field, and in irrigation water at both sites. At one processing facility, wash water pumped from the Rio Grande River may not have been sufficiently disinfected prior to use. Because soil, irrigation water, and process water were potential sources of bacterial contamination, monitoring and management on-farm and at processing and packing facilities should focus on water quality as an important control point for growers and packers to reduce bacterial contamination on melon rinds.     

Combining land use information and small stream sampling with PCR-based methods for better characterization of diffuse sources of human fecal pollution

Diffuse sources of human fecal pollution allow for the direct discharge of waste into receiving waters with minimal or no treatment. Traditional culture-based methods are commonly used to characterize fecal pollution in ambient waters, however these methods do not discern between human and other animal sources of fecal pollution making it difficult to identify diffuse pollution sources. Human-associated quantitative real-time PCR (qPCR) methods in combination with low-order headwatershed sampling, precipitation information, and high-resolution geographic information system land use data can be useful for identifying diffuse source of human fecal pollution in receiving waters. To test this assertion, this study monitored nine headwatersheds over a two-year period potentially impacted by faulty septic systems and leaky sanitary sewer lines. Human fecal pollution was measured using three different human-associated qPCR methods and a positive significant correlation was seen between abundance of human-associated genetic markers and septic systems following wet weather events. In contrast, a negative correlation was observed with sanitary sewer line densities suggesting septic systems are the predominant diffuse source of human fecal pollution in the study area. These results demonstrate the advantages of combining water sampling, climate information, land-use computer-based modeling, and molecular biology disciplines to better characterize diffuse sources of human fecal pollution in environmental waters.     

Quantitative application of fecal sterols using gas chromatography-mass spectrometry to investigate fecal pollution in tropical waters: western Malaysia and Mekong Delta,Vietnam

This is the first report on fecal pollution using molecular markers in Southeast Asia where serious sewage pollution has occurred. A simple and sensitive analytical method using gas chromatography-mass spectrometry for 10 sterols in various environmental samples was developed to monitor extensive areas of tropical Asia. First, the method was applied to wastewater to confirm that >95% of sterols existed in the particulate phase. Then the approach was applied to a tropical Asian region, Malaysia and Vietnam, with a selection of 59 sampling stations in total. River water and sediment samples were collected and analyzed for chemical markers (coprostanol and other sterols) and microbiological markers (fecal coliforms and fecal streptococci). Particulate coprostanol concentrations ranged from <0.0001 to 13.47 microg/L in tropical river and estuarine waters, indicating severe fecal pollution in populous areas. Coprostanol concentrations in the sediments ranged from 0.005 to 15.5 microg/g-dry. The sedimentary coprostanol concentrations were lower than those reported in some urban areas of industrialized countries. This is probably because frequent heavy rain induces intensive input of eroded soil, which dilutes fecal material in river sediments. The relationship between the concentrations of fecal sterols and bacterial indicators was examined in an attempt to develop public health criteria for coprostanol levels applicable to the tropical region. Coprostanol concentrations of 30-100 ng/L or percent coprostanol levels of 2% corresponded to approximately 1000 fecal coliforms per 100 mL, which is set for secondary contact limit in many countries. These coprostanol concentrations were lower than those proposed as criteria in temperate countries, probably owing to greater survival of bacteria in warmer tropical waters. On the basis of these criteria, extensive monitoring of sediments suggests that poor sanitary conditions exist in most of the urbanized area of Malaysia and in several urban and rural sites in Vietnam.