Elevated Moisture Conditions Research Articles

Modeling microbial growth in carpet dust exposed to diurnal variations in relative humidity using the "Time-of-Wetness" framework.

Resuspension of microbes in floor dust and subsequent inhalation by human occupants is an important source of human microbial exposure. Microbes in carpet dust grow at elevated levels of relative humidity, but rates of this growth are not well established, especially under changing conditions. The goal of this study was to model fungal growth in carpet dust based on indoor diurnal variations in relative humidity utilizing the time‐of‐wetness framework. A chamber study was conducted on carpet and dust collected from 19 homes in Ohio, USA and exposed to varying moisture conditions of 50%, 85%, and 100% relative humidity. Fungal growth followed the two activation regime model, while bacterial growth could not be evaluated using the framework. Collection site was a stronger driver of species composition (P = 0.001, R 2 = 0.461) than moisture conditions (P = 0.001, R 2 = 0.021). Maximum moisture condition was associated with species composition within some individual sites (P = 0.001‐0.02, R 2 = 0.1‐0.33). Aspergillus, Penicillium, and Wallemia were common fungal genera found among samples at elevated moisture conditions. These findings can inform future studies of associations between dampness/mold in homes and health outcomes and allow for prediction of microbial growth in the indoor environment.

Chloroform fumigation extraction for measuring soil microbial biomass: The validity of using samples approaching water saturation

The chloroform fumigation-extraction method for determining soil microbial biomass is commonly applied at soil moisture (SM) levels of 40–50% water-holding capacity (WHC). Below that moisture range, restricted enzymatic autolysis might limit the fumigation flush of extractable cellular material, thus underestimating microbial biomass. Likewise, the upper range of SM (i.e., >50% WHC) is considered problematic due to an alleged reduced fumigation efficiency when vapor diffusivity through soil is reduced. The current investigation demonstrated relatively constant fumigation flushes along a 40–90% WHC moisture gradient alongside unchanging carbon-to-nitrogen flush ratios corresponding to characteristic cellular values. This clearly refuted the proposed reduced fumigation efficiency under elevated moisture conditions, and thus validated the applicability of the method to samples collected moist.

Effectiveness of on-site remediation treatments for framing timber

Weathertightness failures in New Zealand buildings due to the combined effects of cladding choices, design and construction faults and the use of untreated framing timber has led to the so called ‘leaky building syndrome’. The latest estimated cost of the leaky building crisis in New Zealand is about NZ$11 billion.This research was conducted to provide a better understanding of the options of using in-situ preservative treatments for controlling incipient and early decay in framing timber which is still structurally sound when remediating leaky buildings.The research approach involved taking untreated radiata pine sapwood, pre-infecting it with common brown rot fungi either Oligoporus placenta or Gloeophyllum sepiarium, applying a brush-on timber treatment of either boron-glycol or copper naphthenate to one or more sides, and then maintaining the samples at elevated moisture conditions. After specific durations, the samples were examined and tested to determine the effectiveness of the treatments in slowing down or preventing decay from progressing using measurement of stiffness (express as modulus of elasticity) and decay (expressed as an index of condition).Assessment confirmed that the performances of both preservatives improved as more sides of timber were treated. However, there were significant differences in efficacy of both preservatives. Boron applied to three or four side appears to have been effective in preventing decay from progressing. Copper naphthenate at the concentration used has not been successful in preventing decay, regardless of the number of faces treated.The treatment retention in samples treated with boron on three or four sides was about 0.4% (BAE w/w) and 0.65% (BAE w/w) respectively. This is close to or above the cross-sectional retention required by New Zealand H1.2 (interior framing) specification.