Virus-sized particles can be entrapped and concentrated one hundred fold within wetland biofilms (Reprinted from Advances in Environmental Research, vol 3, pg 403-411, 2000)

The re-release of pathogens sequestered into environmental compartments (e. g. sediments) represents a potential health risk and is thus an issue of co ncern with relation to wastewater effluent release and reuse. We investigat ed the potential for virus particle incorporation into biofilms in wetlands treating sewage effluent. Virus-sized (100 nm), fluorescent microspheres w ere slug-dosed into wetland mesocosms (126 L each) at 1.52 x 10(8) mL(-1), to act as virus mimics during a seven month pulse-chase field experiment. M icrosphere densities were monitored by microscopy of water and biofilm samp les. The maximum mean density of microspheres in biofilm was 1.76 x 10(10) mL(-1), a one hundred fold increase above the maximum water column density. Microspheres remained at >1.92 x 10(9) mL(-1) in the biofilm for a period of at least seven months, while being rare in the water column. These findi ngs suggest that environmental biofilms can rapidly accumulate virus-like p articles to densities much greater than those present in the water phase. A lack of gradual particle loss from these biofilms revealed the potential f or pathogens to be released back into the water phase within sloughed biofi lm. This may occur during floods or other disturbances, many months after t he initial entrapment, and result in highly concentrated and heterogeneousl y distributed suspended viral loads.