Abstract
Outbreaks of viral disease in populations exposed to contaminated environments have been reported more frequently in recent years. Published studies had tried to explain virus removal based on soil properties; however, soil minerals and amorphous clay minerals in the soil appear to have been overlooked. This has led to inconclusive and sometimes contradictory outcomes, which have often been compounded by small sample size. This study aims to improve the understanding of virus removal by natural soils, by examining the effect of soil property interactions on virus removal. A set of data analysis procedures was proposed to measure the effects of soil property interactions on the removal of bacteriophage MS2 and 0X174. The effects of crystalline soil minerals and amorphous content of the soils were also considered. Data analysis included univariate multiple linear and logistic regression modelling, partial correlation analysis, and means comparison. A total of 33 soil samples were collected across the county of Surrey, United Kingdom. Soil properties were examined using various physico-chemical tests. The removal of bacteriophage MS2 and 0X174 was assessed using these soils. The results showed that levels of aluminium, soil pH, total organic carbon, amorphous iron, amorphous silicon, and goethite significantly predicted the removal of MS2. For 0X174, it was aluminium, soil pH, free proton, smectite and vermiculite. Aluminium, calcium, amorphous silicon and total nitrogen divided the data into subgroups with the greatest contrast of bacteriophage removal values. Partial correlation analysis showed that calcium moderated the effect of many of the significant soil properties on the removal of both MS2 and 0X174. Verification tests performed as batch experiments using KSF, K10 and nepheline syenite soils supported the finding of the regression models, while further highlighting the importance of amorphous clay minerals on MS2 removal, and iron on 0X174 removal. This study showed that the influence of soil cations, soil minerals, organic matter and amorphous clay minerals should be considered together to explain virus removal in soils. This principle can also be applied to other microorganisms and land usage, in order to improve microbial risk assessment.