Standard Rodent Housing Conditions Produce Significant and Sustained Levels of Particulate Matter

Abstract

While the mass of airborne particulate matter have established health guidelines for humans, similar recommendations are not available for laboratory rodent cages. Several studies have assessed the airborne contaminants produced by laboratory animals at the macroenvironment room level to reduce occupational health hazards for those working in animal facilities. These studies have led to established guidelines for protocols such as frequency of cage changes, animal room ventilation rates, and frequency of animal room air changes. However, microenvironmental cage measurements can differ greatly from the macroenvironmental room measurements. Cage-level particulate matter studies are needed to ensure that the laboratory rodent microenvironment is not having a detrimental effect on animal welfare and validity and relevance of scientific data. The objective of the current study was to assess PM levels produced by common rodent bedding types in bar lid and filter top covered rat cages. PM levels were assessed following artificial manipulation of the bedding (designed to simulate typical rodent activity) and during an hour of activity by two adult rats following a standard cage change using pine, aspen, paper, and corn cob bedding. Simulated activity and rat induced disruption of all types of bedding produced significant and substantial increases in PM (1000-6000 µg/m3 PM2.5), with elevated levels (>50ug/m3) sustained for longer durations in cages with filter tops (5-6 minutes) compared to cages with only bar lids (0-2 minutes). These results indicate that standard laboratory housing conditions produce differentially substantial levels of PM that are likely to impact animal welfare and/or experimental data in animal studies of PM exposure.