26 research outputs found
Sunlight-mediated inactivation of health-relevant microorganisms in water: A review of mechanisms and modeling approaches
Health-relevant microorganisms present in natural surface waters and engineered treatment systems that are exposed to sunlight can be inactivated by a complex set of interacting mechanisms. The net impact of sunlight depends on the solar spectral irradiance, the susceptibility of the specific microorganism to each mechanism, and the water quality; inactivation rates can vary by orders of magnitude depending on the organism and environmental conditions. Natural organic matter (NOM) has a large influence, as it can attenuate radiation and thus decrease inactivation by endogenous mechanisms. Simultaneously NOM sensitizes the formation of reactive intermediates that can damage microorganisms via exogenous mechanisms. To accurately predict inactivation and design engineered systems that enhance solar inactivation, it is necessary to model these processes, although some details are not yet sufficiently well understood. In this critical review, we summarize the photo-physics, -chemistry, and -biology that underpin sunlight-mediated inactivation, as well as the targets of damage and cellular responses to sunlight exposure. Viruses that are not susceptible to exogenous inactivation are only inactivated if UVB wavelengths (280 – 320 nm) are present, such as in very clear, open waters or in containers that are transparent to UVB. Bacteria are susceptible to slightly longer wavelengths. Some viruses and bacteria (especially Gram-positive) are susceptible to exogenous inactivation, which can be initiated by visible as well as UV wavelengths. We review approaches to model sunlight-mediated inactivation and illustrate how the environmental conditions can dramatically shift the inactivation rate of organisms. The implications of this mechanistic understanding of solar inactivation are discussed for a range of applications, including recreational water quality, natural treatment systems, solar disinfection of drinking water (SODIS), and enhanced inactivation via the use of sensitizers and photocatalysts. Finally, priorities for future research are identified that will further our understanding of the key role that sunlight disinfection plays in natural systems and the potential to enhance this process in engineered systems
Small Drains, Big Problems: The Impact of Dry Weather Runoff on Shoreline Water Quality at Enclosed Beaches
Enclosed beaches along urban coastlines are frequent hot spots of fecal indicator bacteria (FIB) pollution. In this paper we present field measurements and modeling studies aimed at evaluating the impact of small storm drains on FIB pollution at enclosed beaches in Newport Bay, the second largest tidal embayment in Southern California. Our results suggest that small drains have a disproportionate impact on enclosed beach water quality for five reasons: (1) dry weather surface flows (primarily from overirrigation of lawns and ornamental plants) harbor FIB at concentrations exceeding recreational water quality criteria; (2) small drains can trap dry weather runoff during high tide, and then release it in a bolus during the falling tide when drainpipe outlets are exposed; (3) nearshore turbulence is low (turbulent diffusivities approximately 10(-3) m(2) s(-1)), limiting dilution of FIB and other runoff-associated pollutants once they enter the bay; (4) once in the bay, runoff can form buoyant plumes that further limit vertical mixing and dilution; and (5) local winds can force buoyant runoff plumes back against the shoreline, where water depth is minimal and human contact likely. Outdoor water conservation and urban retrofits that minimize the volume of dry and wet weather runoff entering the local storm drain system may be the best option for improving beach water quality in Newport Bay and other urban-impacted enclosed beaches
Impacts of Beach Wrack Removal via Grooming on Surf Zone Water Quality
Fecal indicator bacteria (FIB) are
used to assess the microbial
water quality of recreational waters. Increasingly, nonfecal sources
of FIB have been implicated as causes of poor microbial water quality
in the coastal environment. These sources are challenging to quantify
and difficult to remediate. The present study investigates one nonfecal
FIB source, beach wrack (decaying aquatic plants), and its impacts
on water quality along the Central California coast. The prevalence
of FIB on wrack was studied using a multibeach survey, collecting
wrack throughout Central California. The impacts of beach grooming,
to remove wrack, were investigated at Cowell Beach in Santa Cruz,
California using a long-term survey (two summers, one with and one
without grooming) and a 48 h survey during the first ever intensive
grooming event. FIB were prevalent on wrack but highly variable spatially
and temporally along the nine beaches sampled in Central California.
Beach grooming was generally associated with either no change or a
slight increase in coastal FIB concentrations and increases in surf
zone turbidity and silicate, phosphate, and dissolved inorganic nitrogen
concentrations. The findings suggest that beach grooming for wrack
removal is not justified as a microbial pollution remediation strategy
Bacterial pathogens in Hawaiian coastal streams – associations with fecal indicators, land cover, and water quality. Water Res
Campylobacter Staphylococcus aureus Vibrio Fecal indicator Tropical streams a b s t r a c t This work aimed to understand the distribution of five bacterial pathogens in O'ahu coastal streams and relate their presence to microbial indicator concentrations, land cover of the surrounding watersheds, and physicalechemical measures of stream water quality. Twentytwo streams were sampled four times (in December and March, before sunrise and at high noon) to capture seasonal and time of day variation. Salmonella, Campylobacter, Staphylococcus aureus, Vibrio vulnificus, and V. parahaemolyticus were widespread d12 of 22 O'ahu streams had all five pathogens. All stream waters also had detectable concentrations of four fecal indicators and total vibrio with log mean AE standard deviation densities of 2.2 AE 0.8 enterococci, 2.7 AE 0.7 Escherichia coli, 1.1 AE 0.7 Clostridium perfringens, 1.2 AE 0.8 F þ coliphages, and 3.6 AE 0.7 total vibrio per 100 ml. Bivariate associations between pathogens and indicators showed enterococci positively associated with the greatest number of bacterial pathogens. Higher concentrations of enterococci and higher incidence of Campylobacter were found in stream waters collected before sunrise, suggesting these organisms are sensitive to sunlight. Multivariate regression models of microbes as a function of land cover and physicalechemical water quality showed positive associations between Salmonella and agricultural and forested land covers, and between S. aureus and urban and agricultural land covers; these results suggested that sources specific to those land covers may contribute these pathogens to streams. Further, significant associations between some microbial targets and physicalechemical stream water quality (i.e., temperature, nutrients, turbidity) suggested that organism persistence may be affected by stream characteristics. Results implicate streams as a source of pathogens to coastal waters. Future work is recommended to determine infectious risks of recreational waterborne illness related to O'ahu stream exposures and to mitigate these risks through control of land-based runoff sources. ª 2011 Elsevier Ltd. All rights reserved. A v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / w a t r e s w a t e r r e s e a r c h 4 5 ( 2 0 1 1 ) 3 2 7 9 e3 2 9 0 0043-1354/$ e see front matter
A Coupled Modeling and Molecular Biology Approach to Microbial Source Tracking at Cowell Beach, Santa Cruz, CA, United States
Consistently
high levels of bacterial indicators of fecal pollution
rank Cowell Beach as the most polluted beach in California. High levels
of fecal indicator bacteria (FIB), <i>E. coli</i> and enterococci,
are measured throughout the summer, resulting in beach advisories
with social and economic consequences. The source of FIB, however,
is unknown. Speculations have been made that the wrack accumulating
on the beach is a major source of FIB to the surf zone. The present
study uses spatial and temporal sampling coupled with process-modeling
to investigate potential FIB sources and the relative contributions
of those sources. Temporal sampling showed consistently high FIB concentrations
in the surf zone, sand, and wrack at Cowell Beach, and ruled out the
storm drain, the river, the harbor, and the adjacent wharf as the
sources of the high concentrations observed in the surf zone. Spatial
sampling confirmed that the source of FIB to the beach is terrestrial
rather than marine. Modeling results showed two dominant FIB sources
to the surf zone: sand for enterococci and groundwater for <i>E. coli</i>. FIB from wrack represented a minor contribution
to bacterial levels in the water. Molecular source tracking methods
indicate the FIB at the beach is of human and bird origin. The microbial
source tracking (MST) approach presented here provides a framework
for future efforts
Cationic Fullerene Aggregates with Unprecedented Virus Photoinactivation Efficiencies in Water
Sunlight-mediated inactivation of health-relevant microorganisms in water: a review of mechanisms and modeling approaches
Health-relevant microorganisms present in natural surface waters and engineered treatment systems that are exposed to sunlight can be inactivated by a complex set of interacting mechanisms. The net impact of sunlight depends on the solar spectral irradiance, the susceptibility of the specific microorganism to each mechanism, and the water quality; inactivation rates can vary by orders of magnitude depending on the organism and environmental conditions. Natural organic matter (NOM) has a large influence, as it can attenuate radiation and thus decrease inactivation by endogenous mechanisms. Simultaneously NOM sensitizes the formation of reactive intermediates that can damage microorganisms via exogenous mechanisms. To accurately predict inactivation and design engineered systems that enhance solar inactivation, it is necessary to model these processes, although some details are not yet sufficiently well understood. In this critical review, we summarize the photo-physics, -chemistry, and -biology that underpin sunlight-mediated inactivation, as well as the targets of damage and cellular responses to sunlight exposure. Viruses that are not susceptible to exogenous inactivation are only inactivated if UVB wavelengths (280–320 nm) are present, such as in very clear, open waters or in containers that are transparent to UVB. Bacteria are susceptible to slightly longer wavelengths. Some viruses and bacteria (especially Gram-positive) are susceptible to exogenous inactivation, which can be initiated by visible as well as UV wavelengths. We review approaches to model sunlight-mediated inactivation and illustrate how the environmental conditions can dramatically shift the inactivation rate of organisms. The implications of this mechanistic understanding of solar inactivation are discussed for a range of applications, including recreational water quality, natural treatment systems, solar disinfection of drinking water (SODIS), and enhanced inactivation via the use of sensitizers and photocatalysts. Finally, priorities for future research are identified that will further our understanding of the key role that sunlight disinfection plays in natural systems and the potential to enhance this process in engineered systems.ISSN:2050-7887ISSN:2050-789