PATHOGEN FATE AND TRANSPORT IN IRRIGATION WATERS
Location: Environmental Microbial and Food Safety Laboratory
Title: Using the Q10 model to simulate the E. coli survival in cowpats on grazing lands
Submitted to: Environment International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 27, 2013
Publication Date: April 1, 2013
Citation: Martinez, G., Pachepsky, Y.A., Shelton, D.R., Whelan, G., Zepp, R., Molina, M., Panhosrt, K. 2013. Using the Q10 model to simulate the E. coli survival in cowpats on grazing lands. Environment International. 54:1-10.
Interpretive Summary: Animal waste on grazing lands can be a source of pathogen and indicator organisms entering surface waters used for irrigation, recreation, and other needs. The importance of this source depends on the survival of microbes in animal depositions. Temperature is known to affect microbe survival in environmental matrices. Our hypothesis was that modeling of E. coli inactivation kinetics in cowpats would be more accurate if temperature was used to correct for rate of inactivation; the rate would be higher (more rapid inactivation) under warm conditions and lower under cold conditions. The Q10 model is widely used to do such corrections in biological systems. We collected all published data on survival of E. coli in cowpats, including experiments in Virginia, Maryland, New Zealand, and United Kingdom, and tested the Q10 model. The
E. coli inactivation rates when adjusted for temperature were remarkably similar among all experiments, and the same set of parameters could be used to model the E. coli inactivation in cowpats in very diverse geographic and management settings. Results of this work will be useful for site-specific evaluation of the effect of grazing on microbial quality of surface water sources.
Microbiological quality of surface water sources can be affected by microbial load in runoff from grazing lands. This effect depends, among other factors, on survival of microorganisms in animal waste deposited at pastures. Temperature is one of leading environmental parameters affecting the survival. The Q10 model is a widely used tool to simulate the effect of temperature on rates of biological processes. The objective of this work were (i) to evaluate the applicability of the Q10 model to the E. coli inactivation in bovine animal waste deposited at grazing land as cowpats, and ii) to identify a set of parameters that could reproduce the previously reported E. coli die-off dynamics in cowpats. The database included published data on E. coli concentrations in natural and repacked cowpats were analyzed in experiments in Virginia, USA, Maryland, USA, New Zealand, and United Kingdom. Inspection of the datasets led to the conceptualizing the field E. coli survival as a two-stage process where the first stage could be growth, inactivation or stationary state of the population, and the second stage was the approximately first-order inactivation. Application of the Q10 model showed the remarkable similarity in inactivation rates defined by using the thermal time. The reference inactivation rate constant of 0.042 (thermal days)-1 at 20°C gave a good approximation (R2=0.88) of all inactivation stage data with Q10 = 1.48. The reference inactivation rate constants in individual experiments were not different from the one obtained using all data pooled together (P < 0.05). The rate of logarithm of E. coli concentration change during the first stage depended on temperature. The duration of the first stage until the first order inactivation started and the initial concentration of E. coli in cowpats could not be predicted from data collected during experiments. Diet and age are probable factors affecting these