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. 2018 Nov 20;52(22):13068-13076.
doi: 10.1021/acs.est.8b02191. Epub 2018 Nov 12.

Biological Weighting Functions for Evaluating the Role of Sunlight-Induced Inactivation of Coliphages at Selected Beaches and Nearby Tributaries

Richard G Zepp  1 , Michael Cyterski  1 , Kelvin Wong  1 , Ourania Georgacopoulos  1 , Brad Acrey  1 , Gene Whelan  1 , Rajbir Parmar  1 , Marirosa Molina  1
Affiliations

Biological Weighting Functions for Evaluating the Role of Sunlight-Induced Inactivation of Coliphages at Selected Beaches and Nearby Tributaries

Richard G Zepp et al. Environ Sci Technol. .

Abstract

Coliphages can indicate contamination of recreational waters and previous studies show that sunlight is important in altering densities of coliphages, other indicator microorganisms, and pathogens in aquatic environments. Here, we report on laboratory studies of light-induced inactivation of two coliphage groups-male-specific (F+) and somatic coliphage-under various conditions in phosphate-buffered water (PBW). Strains isolated from wastewater treatment facilities and laboratory strains (MS2 and phiX174 coliphages) were evaluated. Inactivation rates were determined in a series of irradiations using simulated solar radiation passed through light filters that blocked different parts of the ultraviolet spectral region. Inactivation rates and spectral irradiance from these experiments were then analyzed to develop biological weighting functions (BWFs) for the light-induced inactivation. BWFs were used to model the inactivation of coliphages over a range of conditions in aquatic environments that included two beach sites in Lake Michigan and one in Lake Erie. For example, modeled effects of sunlight attenuation, using UV absorption data from the three Great Lakes beach sites, inferred that direct photoinactivation rate constants, averaged over a one-meter water column in swimmable areas, were reduced 2- to 5-fold, compared to near-surface rate constants.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1.
Figure 1.
(A) First-order rate constants (ki × 103, s−1) for photoinactivation observed with radiation in a solar simulator filtered by various UV-cutoff filters (see the Experimental Section and the Supporting Information): blue circles, phiX174; green circles, NE OH somatic; red circles, NE OH F+; black circles, MS2; (B) First order rate constants with 305 nm cutoff filter for the photoinactivation of phiX174 in samples used in this study. There was no statistically significant change in the first order rate constants with dilution by PBW, indicating that residual broth was not sensitizing phage photoinactivation.
Figure 2.
Figure 2.
Biological weighting functions for photoinactivation of coliphages normalized to unity at 300 nm, compared to the normalized DNA action spectrum (Setlow 1974).(52) Plotted values are for MS2 (black line), NE OH F+ (red), NE OH somatic (green), phiX174 (blue) and Setlow DNA action spectrum (cyan).
Figure 3.
Figure 3.
Comparison of the BWF (black line, normalized to its value at 300 nm) for somatic coliphages isolated from a Northeast Ohio wastewater treatment plant and near-surface solar spectral irradiance during mid-July at Washington Park Beach (red line). Weighted irradiance (dashed green line, normalized to its maximum value) peaked at about 308 nm.
Figure 4.
Figure 4.
Comparison of inactivation rate constants for MS2: A) BWFs for MS2 photoinactivation determined by Fisher et al.(35) (red line) and this study (black line); B) photo inactivation rate constants (ki) for MS2 estimated using BWFλ and solar spectral irradiance (black bars)) and observed (red bars) in either solar simulator or natural sunlight as noted above. Data are derived from Love et al.,(7) Fisher et al.,(35) Silverman et al.,(32) Nguyen et al.,(27) and this study.
Figure 5.
Figure 5.
Potential latitudinal variation in diurnal photoinactivation rate constants for somatic coliphage isolated from a Northeast Ohio wastewater treatment plant. Latitude 20°N (black); latitude 40° N (red); latitude 60° N (blue).
Figure 6.
Figure 6.
Simulated depth dependence for direct photoinactivation of coliphages at mid-day, July 15, 2015 in beach water located in Washington Park (Michigan City, IN). MS2 (filled black circles); NE OH F+ (red); NE OH somatic (green); phiX174 (blue). Dashed lines are 95% confidence intervals based on a Monte Carlo simulation. Average ki (s−1) over a one-meter water column: MS2 (0.139 × 10−4); NE Ohio F+ (0.408 × 10−4); NE Ohio Somatic (0.846 × 10−4); phiX174 (1.33 × 10−4).
Figure 7.
Figure 7.
Simulated depth dependence of coliphage photoinactivation in beach waters and their tributaries in the Great Lakes. Bars represent ratios of photoinactivation rates at the surface to rates averaged over a one-meter deep water column: A) ratios in swimmable areas of beaches located at Edgewater Park in Lake Erie near Cleveland OH (red); Grant Park (South Milwaukee, WI) on Lake Michigan (green), and Washington Park (Michigan City, IN) on Lake Michigan (blue). B) ratios in tributaries of beaches located at Edgewater Park (red); Grant Park (green); and Washington Park (blue). The much larger bars for the tributaries indicates the higher levels of UV protection provided to coliphages and other microorganisms in these systems.(40)
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