Table 3.

Factors influencing microbial fate in the subsurface

Factor	Influence on
	Survival	Transport
Temperature	Longer survival at lower temperatures	Unknown
Microbial activity	Variable, depending on microorganism type and environmental conditions	Unknown
Dissolved oxygen	Variable results have been reported	Unknown
Organic matter	May protect microorganism from inactivation; other studies have shown that it may reversibly retard virus infectivity	Soluble organic matter competes with microorganisms for adsorption sites on soil particles
Microorganism type	In general, helminths survive the longest, followed by viruses and parasites, whereas bacterial survival is generally the lowest	Larger microorganisms are removed more easily; thus, viruses have the highest potential for transport, followed by the bacteria; parasites are often too large to be transported great distances
Aggregation	Generally enhances survival	Retards movement, due to larger particle size
pH	Varies depending on microorganism, but survival tends to be best at near-neutral pH values; many enteric viruses are stable over a pH range of 3–9	Varies, depending on isoelectric point of the microorganism; generally, low pH favors adsorption, and high pH results in desorption
Moisture content	Many microorgansims persist longer in soils with higher moisture content	Transport is greater under saturated than unsaturated conditions
Adsorption to soil	Variable results have been reported	Movement is slowed or prevented
Soil properties	Effects on survival are likely related to degree of adsorption to soil	Greater migration occurs in coarse-textured soils; retention is created in soils containing clay

Source: Yates MV and Yates SR (1987) Modeling microbial fate in the subsurface environment. CRC Critical Reviews in Environmental Control 17: 307–344.