Association with natural organic matter enhances the sunlight-mediated inactivation of MS2 coliphage by singlet oxygen.
MS2 coliphage, a surrogate for human enteric viruses, is inactivated by singlet oxygen (1O2) produced via sunlight-mediated excitation of natural organic matter (NOM) in surface waters. The 1O2 concentration within a NOM macromolecule or supramolecular assembly ([1O2]internal) is orders of magnitude higher than in the bulk solution ([1O2]bulk). In close proximity of NOM, MS2 is thus exposed to an elevated 1O2 concentration ([1O2]NOM), and inactivation is likely to be enhanced as compared to the bulk solution. In experiments using a solar simulator, we determined [1O2]bulk, [1O2]internal, as well as the association of MS2 with four NOMs (Fluka humic acid, FHA; Suwannee river humic acid, SRHA; Aldrich humic acid, AHA; Pony lake fulvic acid, PLFA), and studied their effect on the MS2 inactivation rate constant, k(obs), over a range of 1-25 mg NOM/L. The k(obs) values were modeled as the sum of the inactivation rate constants in close proximity to the NOM and in the bulk solution, assuming Langmuir-type adsorption of NOM onto MS2. FHA and SRHA exhibited 13-22 fold greater adsorption equilibrium constants than AHA and PLFA. Inactivation in the bulk solution contributed between 2% (20 mg/L FHA) and 39% (5 mg/L AHA) toward the overall k(obs). Thus, even for the less adsorbing NOM, inactivation was dominated by [1O2]NOM rather than [1O2]bulk. Changes in solution chemistry to promote closer interactions between MS2 and NOM also enhanced k(obs). Addition of Mg2+ to neutralize the negative surface charge of MS2 and NOM increased k(obs) up to 4.1-fold. Similarly, lowering the solution pH closer to the isoelectric point of MS2 (pl = 3.9) enhanced k(ob), 51-fold in 5 mg/L AHA.
Kohn
Tamar
T
Department of Civil and Environmental Engineering, University of California, Berkeley, California 94720, USA. tamar.kohn@epfl.ch
Grandbois
Matthew
M
McNeill
Kristopher
K
Nelson
Kara L
KL
D017909:Levivirus / Q000737:chemistry / Q000528:radiation effects*; D009930:Organic Chemicals / Q000737:chemistry*; D026082:Singlet Oxygen / Q000737:chemistry*; D013472:Sunlight
D009930:Organic Chemicals; D026082:Singlet Oxygen