Solar Inactivation Research Articles

Visible light photocatalytic response of Fe doped TiO2: Inactivation of Escherichia coli

Heterogeneous photocatalysis has been widely investigated for the removal of pollutants and pathogenic microorganisms. Various modified photocatalysts were developed for the beneficial use of solar light. E. coli inactivation by Fe doping of TiO2 (P-25) and sol–gel prepared (SynTiO2) was achieved upon solar irradiation in both isotonic (IsoT) and water matrix (WM) conditions. First order kinetic rate constants were comparatively higher for bare SynTiO2 both in IsoT (k = 0.254 min−1) and WM (k = 0.180 min−1) solutions. WM exerted an overall retardation effect for all photocatalysts except for 0.50 % Fe-TiO2 and 0.25 % Fe-SynTiO2. Release of intracellular components was followed by spectroscopic parameters as well as dissolved organic carbon (DOC) contents. E. coli cell destruction was related to the released protein, carbohydrate, and K+ ion contents. Solar photocatalytic inactivation of E. coli using novel sol–gel prepared TiO2 and Fe doped sol–gel TiO2 was successfully demonstrated as an alternative and promising method for disinfection purposes.

Evaluating the aeration efficiency of hydraulic flume on photo-oxidative disinfection of wastewater

Photosensitized oxidation has been considered to offer better disinfection mechanism under natural sunlight and the efficiency of its inactivation pathway depends on the concentration of dissolving oxygen, the solar irradiance, and the reactive nature of the liquid. This study aimed to evaluate the hydraulic mixer's aeration performance during photo-oxidation treatment. A hydraulic jump was created to aerate the sewage prior to its passage into a reactor, and the amount of dissolved oxygen generated was measured. The effect of mixing intensity on sunlight inactivation of faecal coliforms in a reactor was investigated for 60 min using velocity gradients of 520 s−1, 640 s−1, 720 s−1 and 960 s−1 produced under flow rates of 3 L min−1, 5 L min−1 and 7 L min−1 and 10 L min−1 respectively. The photo-oxidation kinetics of faecal coliform contained in settled and raw sewage samples were also studied under two dark control tests (static and dynamic tests) and a light test. The system achieved a 2.0–2.34 log reduction of faecal coliforms and dissolved oxygen was within the range of 1.9 mg L−1 - 3.0 mg L−1. In the dynamic control test, the inactivation rate constant of bacteria indicated a reduction of 1.11 log (92%) for settled sewage and 1.0 log (90%) for raw sewage. The coliform inactivation rate constant, due to the combined effect of turbulent mixing speed and dark inactivation rate constant, was 2.3 h−1, and the solar irradiance inactivation rate constant was 2.4 h−1. These results have demonstrated that induced aeration is an economically friendly approach to enhance wastewater treatment in developing nations with long sunshine hours.

Experimental feasibility study of multipurpose low-cost solar thermal device for different applications including inactivation of SARS CoV-2

This study show the experimental feasibility of the Solar thermal energy-based disinfection and inactivation of viruses, including the SARS CoV-2 from the different surfaces and utensils. A small prototype device is proposed and fabricated to serve the purpose. This device was tested in the field conditions using cotton clothes as a material/surface/utensil to observe the heating performance of the proposed device to attain the desired temperature range and corresponding timeline of heat-based 4 and 5 log viral load reduction/inactivation protocol. A new parameter ‘Disinfection Power’ is proposed to comment on the thermal performance of the SDC.The SDC satisfactorily reached temperatures ∼75–80 °C required for the 4 and 5 log heat-based viral load reduction protocol for disinfection cycles and maintained it for the heat for desired time line of minimum 60 min for the rated load of utensils. The value of the disinfection power at mean temperature difference (25 °C in the present case) is 29.9 W. The exergy efficiency of the SDC shows variation between 12.62 % and 22.69 %. Thus, SDC offers an affordable solution to reduce the risk of spreading the virus through contact with clothes and utensils.

Enhanced solar inactivation of fungal spores by addition of low-dose chlorine: Efficiency and mechanism

This work demonstrated that the solar inactivation of fungal spores was enhanced by addition of low-dose chlorine. Although the effect of low-dose chlorine alone (2.0 mg/L) on culturability of fungal spores was negligible, the solar/chlorine inactivation on fungal spores performed better than solar alone inactivation, with a lower shoulder length and a higher maximum inactivation rate constant. The enhanced inactivation of Aspergillus niger can be ascribed to the membrane oxidation by chlorine, and the enhanced inactivation of Penicillium polonicum can be ascribed to the membrane oxidation by chlorine and ·OH (·OH plays a major role). The oxidization by chlorine and ·OH led to an increase in membrane permeability of fungal spores, which enhanced the solar inactivation, resulting in an increase in intracellular ROS and more serious morphological damage. Due to the presence of background substances such as dissolved organic matter and metal ions (Fe2+, Mn2+, etc.), the inactivation efficiency in real water matrices was decreased. The main disinfection by-products (DBPs) produced in the inactivation of fungal spores in chlorine alone and solar/chlorine treatments were dichloroacetic acid, trichloroacetic acid, trichloroacetone and trichloromethane. Generally, DBPs formation in solar/chlorine treatment was lower than those in chlorine alone treatment. Moreover, the regrowth potential of the two genera of fungal spores in R2A medium could be inhibited by adding low-dose chlorine.

Mechanistic modelling of solar disinfection (SODIS) kinetics of Escherichia coli, enhanced with H2O2 – Part 2: Shine on you, crazy peroxide

In this second part of the development of a mechanistic kinetic model of the solar inactivation of E. coli enhanced with hydrogen peroxide, we evaluate the mechanisms based on photonic inactivation and integrate them into the kinetic model of the dark process developed in Part 1. The direct photonic inactivation was modelled using a series-event model based on the accumulation of damage by photons and it was coupled with the model used in Part 1 for modelling the damage caused by radicals using a multiple target – multiple hit model, including recovery constant to define the ability of cells to face the specific photonic damage. Catalase and superoxide dismutase inactivation, the intracellular photo-Fenton reaction, and the overproduction of O2•- in the NADH/NAD+ cycle under solar light were included in the model. Finally, the synergistic effect of the photonic damage with thermal inactivation was included in the kinetic constant of the series-event expression in terms of an Arrhenius equation. The kinetic parameters were obtained by model regression using experimental data at different temperatures, solar radiation, as well as initial cellular and H2O2 concentrations. Our model predictions can accurately describe the experimental data of the SODIS process enhanced with H2O2, thus being very useful to estimate disinfection profiles and inactivation routes at different irradiance conditions, water temperature and H2O2 concentration. Finally, an integrated mechanism of E. coli inactivation under the SODIS/H2O2 process is provided.

Effect of pH on endogenous sunlight inactivation rates of laboratory strain and wastewater sourced E. coli and enterococci.

Understanding the influence of environmental factors like pH on solar disinfection in sunlight-dependent wastewater treatment systems can aid in improving their design. Previous research found pH to influence the solar disinfection rates of bacteria in water containing exogenous photosensitizers that facilitate photo-oxidative inactivation. However, limited research has been conducted on the role of external pH on endogenous solar inactivation processes that occur independent of exogenous photosensitizers. As such, we studied the inactivation rates of laboratory-cultured and wastewater-sourced E. coli and enterococci in sensitizer-free matrices with pH ranging from 4 to 10 under full-spectrum and UVB-filtered simulated sunlight. Elevated solar inactivation rates were observed at pH 4 for all bacterial populations evaluated, and at pH 10 for laboratory-cultured and wastewater-sourced E. coli. Dark inactivation was observed at the pH extremes for some bacteria, but did not contribute significantly to the increased inactivation rates observed under simulated sunlight at these pH, except for laboratory-cultured E. coli at pH 10. UVB light was found to play an important role in sunlight inactivation, albeit the contribution of UVB light to solar inactivation observed for Enterococcus spp. diminished at pH 4 and 5, suggesting that indirect endogenous inactivation pathways facilitated by longer wavelength light were enhanced under acidic conditions. Our findings demonstrate that external pH affects the kinetics of endogenous sunlight inactivation processes, and the results have potential to be integrated into models for predicting inactivation kinetics in sunlight-mediated treatment systems that operate over a range of pH conditions.

Photocatalytic Bactericidal Performance of LaFeO3 under Solar Light in the Presence of Natural Organic Matter: Spectroscopic and Mechanistic Evaluation

Solar photocatalytic inactivation (SPCI) of E. coli as the indicator microorganism using LaFeO3 (LF) has already been investigated under various experimental conditions, excluding any role of natural organic matter (NOM). However, comprehensive information about the behavior of E. coli and its inactivation mechanism in the presence of NOM, as well as the behavior of NOM components via solar photocatalysis using LF as a photocatalyst, has prime importance in understanding real natural water environments. Therefore, in this study, further assessment was devoted to explore the influence of various NOM representatives on the SPCI of E. coli by using LF as a novel non-TiO2 photocatalyst. The influence of NOM as well as its sub-components, such as humic acids (HA) and fulvic acids (FA), was also investigated to understand different NOM-related constituents of real natural water conditions. In addition to spectroscopic and mechanistic investigations of cell-derived organics, excitation emission matrix (EEM) fluorescence spectra with parallel factor multiway analysis (PARAFAC) modeling revealed further information about the occurrence and/or disappearance of NOM-related and bacteria-related fluorophores upon LF SPCI. Both the kinetics as well as the mechanism of the LF SPCI of E. coli in the presence of NOM compounds displayed substrate-specific variations under all conditions.

Solar disinfection of fungal spores in water: Kinetics, influencing factors, mechanisms and regrowth

Water contamination with fungi has gained attention increasingly, while solar disinfection (SODIS) is a potential method, especially for developing countries. In this work, inactivation kinetics, influencing factors, mechanisms and regrowth of fungal spores in the SODIS process were firstly investigated. The inactivation fitted well with the Geeraerd and Van Impe inactivation model-fitting tool and P. polonicum was more sensitive to simulated sunlight than A. niger. The pH value within the range of 5–9 and low concentration humic acid did not affect the solar inactivation of fungal spores, while HA at the concentration above 5.0 mg/L inhibited the solar inactivation efficiency. Over the tested range, the inactivation efficiency was obtained at the temperature near the optimal growth temperature (30-40 °C for A. niger, 20–30 °C for P. polonicum). According to the results of flow cytometry, ATP concentration and scanning electron microscopy, the solar inactivation of fungal spores was ascribed to endogenous actions. During the SODIS process, the DNA and respiratory chain of fungal spores were attacked. Subsequently, esterase activity was induced. As a result, the spores lost the culturability firstly, accompanied by the exhaustion of ATP, finally the membrane became permeable. Although no fungal spore regrowth was observed in ground water and surface water after SODIS, they remained a certain regrowth potential in nutrient-rich water like R2A. This work uncovered the control of waterborne fungi by SODIS.

Elucidation of in-situ produced organic matrix effect on the solar photo/photocatalytic inactivation of E. coli

Solar photoinactivation and photocatalytic inactivation of E. coli in aqueous solution was investigated in various matrix conditions in the presence/absence of humic acid as representative of natural organic matter and inorganic components focusing on the spectroscopic evaluation of in-situ produced organic matrix. Characterization of organic matter with respect to E. coli inactivation under various experimental conditions was followed by the elucidation of specified UV–vis and fluorescence parameters as well as dissolved organic carbon content. Solar light initiated destruction of bacterial cells via lysis were visualized by the occurrence of protein-like fluorophores and fluorophores of microbial by-products as presented in excitation emission matrix fluorescence contour plots indicating a variety of changes in their shape and intensity with respect to increasing irradiation periods. Moreover, under similar experimental conditions, in the presence of humic matter these fluorophores were mainly quenched by humic-like fluorophores.E. coli inactivation kinetics obeyed first order kinetic model for both solar photoinactivation and photocatalytic inactivation conditions. Rate constants for photoinactivation of E.coli ranged from 0.184 to 0.0920 min−1, whereas photocatalytic inactivation rate constants varied from 0.248 to 0.0488 min−1. Both humic acid and water matrix components had inhibitory effects on inactivation efficiency which could be attributed to competitive reactions occurring between humic matter, bacterial cells, and bacteria derived organic material. Further evaluation of bacteria inactivation was followed by detection of organic (protein and carbohydrate) and inorganic (K+ leakage) constituents under specified conditions in correlation to the spectroscopic parameters.

Photocatalytic Bactericidal Performance of LaFeO3 under Solar Light: Kinetics, Spectroscopic and Mechanistic Evaluation

Lanthanum orthoferrites are a versatile class of catalysts. Here, the photocatalytic bactericidal performance of LaFeO3 (LF) to inactivate pathogenic microorganisms, i.e., Escherichia coli (E. coli), in water under simulated solar irradiation conditions was investigated. Various competing and contributing factors were covered to visualize the reaction medium consisting of E. coli K12 cells, organic sub-fractions formed by cell destruction, and LF surface. LF solar photocatalytic inactivation (SPCI) kinetics revealed the highest inactivation rate in ultrapure water as expected, followed by distilled water (DW), aqueous solution containing anions and cations (WM) and saline solution (SS). Characterization of the released organic matter was achieved by UV-vis and fluorescence spectroscopic techniques as well as organic carbon contents (DOC). Upon SPCI, significant amounts of K+ along with released protein contents were detected expressing cell wall destruction and lysis. Under the specified experimental conditions, in the presence of released intracellular organic and inorganic components via cell lysis, a significant count of E. coli was still present in SS, whereas almost all bacteria were removed in other matrices due to various challenging reasons. Based on the presented data, SPCI of E. coli using LF as a novel photocatalyst was successfully demonstrated as an alternative and promising method for disinfection purposes.

Seasonal Effect of Sunlight on COVID-19 among Countries with and without Lock-Downs

Objective: The main aim of the study was to determine whether COVID-19 epidemiological data reported by countries in different hemispheres correlated with the seasons of the year. Since stay-at-home orders could be a main factor affecting the time individuals spent outdoors, the progression of COVID-19 in countries that mandated the most stringent lock-downs and stay-at-home orders was compared to countries in the same hemisphere that did not order their citizens to remain at home. Methods: Infections attributed to COVID-19 per million inhabitants, deaths per infections × 100, and deaths per million inhabitants from different countries were analyzed utilizing national reports registered in the Johns’ Hopkins database together with the most recent world population data. The null hypothesis (no difference between countries with and without lock-downs) was tested (two tailed test, p Results: The shift of highest infection rates from countries in the northern-towards countries in the southern-hemisphere during early 2020 and the reverse in December of the same year correlates with the seasonal variation in the flux of germicidal sunlight. Mortality rate for the same virus among different countries did not show a seasonal component. COVID-19 infection mortality rate was considerably lower in developing countries of South America (11 of the largest countries) than in several (at least 8) developed European countries. Discussion: COVID-19 resulted in higher infections during winter than in summer. The finding of a seasonal component, correlating the progression of the pandemic with local solar flux, demonstrates that infectious virus in the environment plays a role in the pandemic since direct person-to-person transmission would afford little time for solar inactivation. Similar epidemiological data amongst “locked” and “unlocked” countries demonstrates that lock-downs and similar confining measures had no effect on the chances of healthy individuals becoming infected with SARS-CoV-2 or dying of COVID-19.

Photocatalytic degradation of pharmaceutically active compounds (PhACs) in urban wastewater treatment plants effluents under controlled and natural solar irradiation using immobilized TiO2

The degradation of pharmaceutically active compounds (PhACs) under controlled and natural solar irradiation using immobilized TiO2 was studied in model solution and real urban wastewater effluents. The TiO2 coatings were prepared via the sol–gel method with two different configurations, using simple (thin films) and the “sandwich” approach. Prepared coatings were characterized employing X-ray diffraction (XRD), scanning electron microscopy (SEM), ellipsometry and UV–Vis diffuse reflectance spectroscopy. Decomposition of PhACs detected in urban wastewater effluents (diclofenac, carbamazepine, atenolol, propranolol, albuterol, ofloxacin, ciprofloxacin, azithromycin, erythromycin, hydrochlorothiazide, and furosemide) was monitored using Ultra Performance Liquid Chromatography-Triple Quadrupole Mass Spectrometry (UPLC-QqQ-MS/MS). Among detected PhACs three are included in the Watch List (EU Decision 2018/840). The “sandwich” coatings (deposited on frosted support) with the following structure: anatase layer, TiO2 P25 nanoparticles and anatase layer (sealing film) demonstrated the highest photocatalytic activity among all tested TiO2 coatings and were used for elimination of PhACs from real urban wastewater effluents. Photocatalytic treatment of urban wastewater effluents under controlled and natural solar irradiation led to moderate and high removal (>40%) of all detected PhACs except carbamazepine and atenolol, for which poor removal efficiency was observed (~20%). Some of the PhACs compounds present in wastewater effluents, such as diclofenac, ofloxacin, ciprofloxacin, hydrochlorothiazide and furosemide were sensitive to solar photolysis. The efficiency of solar photocatalytic inactivation of Escherichia coli present in urban wastewater effluent was similar to that of solar disinfection (SODIS).

Mechanistic modelling of wastewater disinfection by the photo-Fenton process at circumneutral pH

This work focuses, for the first time, on the mechanistic modelling of wastewater disinfection by the solar photo-Fenton process using controlled solar simulated radiation. At circumneutral pH, iron precipitates forming hydroxides and significantly affecting the optical properties of the water. In this regard, radiation transfer in the reactor has been taken into account. The proposed model considers that the solar inactivation of bacteria follows a serial n-event mechanism with n reversible steps of photonic attacks leading to the bacterial inactivation. Dark Fenton cyclic process of hydroxyl radical formation from hydrogen peroxide is considered to be mediated mainly by precipitated iron species, prevailing at circumneutral pH. Finally, the photo-Fenton process was modelled using a multiple target – multiple hit mechanistic approach that accounts for the synergistic effect between the photonic and the hydroxyl radical attacks to the bacteria. Model predictions successfully reproduce experimental data of solar disinfection, hydrogen peroxide consumption, and photo-Fenton disinfection at circumneutral pH.

Estimated Inactivation of Coronaviruses by Solar Radiation With Special Reference to COVID-19.

Using a model developed for estimating solar inactivation of viruses of biodefense concerns, we calculated the expected inactivation of SARS‐CoV‐2 virus, cause of COVID‐19 pandemic, by artificial UVC and by solar ultraviolet radiation in several cities of the world during different times of the year. The UV sensitivity estimated here for SARS‐CoV‐2 is compared with those reported for other ssRNA viruses, including influenza A virus. The results indicate that SARS‐CoV‐2 aerosolized from infected patients and deposited on surfaces could remain infectious outdoors for considerable time during the winter in many temperate‐zone cities, with continued risk for re‐aerosolization and human infection. Conversely, the presented data indicate that SARS‐CoV‐2 should be inactivated relatively fast (faster than influenza A) during summer in many populous cities of the world, indicating that sunlight should have a role in the occurrence, spread rate and duration of coronavirus pandemics.

Numerical Modeling of Microbial Fate and Transport in Natural Waters: Review and Implications for Normal and Extreme Storm Events

Degradation of water quality in recreational areas can be a substantial public health concern. Models can help beach managers make contemporaneous decisions to protect public health at recreational areas, via the use of microbial fate and transport simulation. Approaches to modeling microbial fate and transport vary widely in response to local hydrometeorological contexts, but many parameterizations include terms for base mortality, solar inactivation, and sedimentation of microbial contaminants. Models using these parameterizations can predict up to 87% of variation in observed microbial concentrations in nearshore water, with root mean squared errors ranging from 0.41 to 5.37 log10 Colony Forming Units (CFU) 100 mL−1. This indicates that some models predict microbial fate and transport more reliably than others and that there remains room for model improvement across the board. Model refinement will be integral to microbial fate and transport simulation in the face of less readily observable processes affecting water quality in nearshore areas. Management of contamination phenomena such as the release of storm-associated river plumes and the exchange of contaminants between water and sand at the beach can benefit greatly from optimized fate and transport modeling in the absence of directly observable data.

Kinetic modeling of the synergistic thermal and spectral actions on the inactivation of viruses in water by sunlight

Sunlight can be an effective tool for inactivating pathogens in water disinfection processes. In clear water, photoinactivation of viruses is driven by the absorption of UVB radiation and it is more efficient at shorter wavelengths. Moreover, the temperature can significantly improve the efficiency of the process. To date, no kinetic model has been reported that describes the simultaneous thermal and spectral effects that occur during the solar inactivation of viruses. This work presents a novel comprehensive kinetic model for the solar inactivation of MS2 coliphage as a function of the water temperature, irradiance, and spectral distribution of the incident radiation. The model is based on a combination of the modified Arrhenius equation, a wavelength-dependent first-order inactivation model with the quantum yield, and thermal parameters estimated from laboratory data. Model predictions have a 9% error with respect to experiments in the temperature range from 30 to 50 °C and UV irradiance range from 15 to 50 W/m2. Moreover, the model was validated in three scenarios using different plastic materials that modify the spectral range of the radiation reaching the water, confirming an accurate prediction of inactivation rates for real solar disinfection systems worldwide using containers made of any material.

Efficacy of a solar concentrator to Inactivate E. coli and C. perfringens spores in latrine waste in Kenya.

Alternative sanitation options are needed for effective waste management in low-income countries where centralized, large-scale waste treatment is not easily achievable. A newly designed solar concentrator technology utilizes solar thermal energy to treat feces contained in drums. This pilot study assessed the efficacy of the new design to inactivate microbes in 13 treatment drums under field conditions in Kenya. Three-quarters of the drums contained <1000 E. coli/g of total solids following 6 h of solar thermal treatment and inactivation of thermotolerant C. perfringens spores ranged from <1.8 to >5.0 log10. Nearly all (94%) samples collected from treatment drums achieved thermophilic temperatures (>50 °C) during the treatment period, however this alone did not ensure samples met the WHO E. coli guideline; higher, sustained thermophilic temperatures tended to be more effective in reaching this guideline. The newly designed solar concentrator was capable of inactivating thermotolerant, environmentally-stable microorganisms as, or possibly more, efficiently than a previous design. Additional data are needed to better characterize how temperature, time, and other parameters affect the ability of the solar concentrator to inactivate microbes in feces.

Comparative Study of Solar Inactivation of Total Coliforms through Transparent Plastic Bottles and Fabricated Disinfection Setup

The water is disinfected through different techniques commonly used at domestic level, including boiling, chlorination, UV (Ultraviolet) disinfection, etc. These methods require extensive amount of chemicals, energy and trained manpower. The solar disinfection of drinking water found as best among all other disinfection techniques as it is easy to apply, economically feasible and environmentally friendly technique. In this study a series of experiments were conducted in order to characterize the bacterial inactivation process contained in FDS (Fabricated Disinfection Setup), consists of a stainless steel tub and glass covering, and TPB (Transparent Plastic Bottles). In this study the role of solar radiation in bacterial inactivation process is compared in transparent plastic bottles and stainless steel tub to determine the performance of both by simulating conditions of turbidity, temperature, and exposure time. The results showed that disinfection of water contained in a stainless steel tub promoted more successful inactivation of total Coliforms reduction about 80% than that of transparent plastic bottles about 70%.

Kinetic study of Z-scheme C3N4/CuWO4 photocatalyst towards solar light inactivation of mixed populated bacteria

In the present work, Z-scheme composite C3N4/CuWO4 was synthesised by sol-gel method for the photocatalytic degradation of a mixed population of Gram-positive bacteria (S. aureus) and Gram-negative bacteria (E. coli). The effect of the photoinactivation was observed for two different types of bacteria in the same medium together and individually in the absence of the nutrients. The lattice structures and phase purities were determined by X-ray diffraction. For morphological and topographical features, SEM and TEM imaging were performed. The oxidation states of the elements and band edges of the semiconductor were determined by XPS and UPS, respectively. The lifetime of the charge carriers and band gap of the semiconductors were determined by time resolved florescence spectroscopy and diffused reflectance spectroscopy, respectively. The photocatalytic experiments were performed for different weight ratios of C3N4 and CuWO4. Scavenger experiments were performed to investigate the exact mechanism and major responsible radicals for photocatalysis. The rate constants and order of the inactivation reactions were obtained by power law kinetics. The rate followed by the inactivation for E. coli and S. aureus were analysed. For E. coli, the order of inactivation reaction is 1.15 while S. aureus inactivation reaction order is 0.9.

Climate change-induced increases in precipitation are reducing the potential for solar ultraviolet radiation to inactivate pathogens in surface waters

Climate change is accelerating the release of dissolved organic matter (DOM) to inland and coastal waters through increases in precipitation, thawing of permafrost, and changes in vegetation. Our modeling approach suggests that the selective absorption of ultraviolet radiation (UV) by DOM decreases the valuable ecosystem service wherein sunlight inactivates waterborne pathogens. Here we highlight the sensitivity of waterborne pathogens of humans and wildlife to solar UV, and use the DNA action spectrum to model how differences in water transparency and incident sunlight alter the ability of UV to inactivate waterborne pathogens. A case study demonstrates how heavy precipitation events can reduce the solar inactivation potential in Lake Michigan, which provides drinking water to over 10 million people. These data suggest that widespread increases in DOM and consequent browning of surface waters reduce the potential for solar UV inactivation of pathogens, and increase exposure to infectious diseases in humans and wildlife.