Fragmentation of Cotton Bract and a Technique for Detecting Bract in Cotton Dust1

Abstract

AbstractBract fragments are thought to be a major component of the respirable dust generated during the processing of cotton (Gossypium sp.) lint in textile mills. Byssinosis is an occupational disease affecting susceptible textile workers exposed to respirable dust. Procedures designed to reduce mill dust require that the dust components be identified. The cotton bract is a candidate component. The objectives of this study were (A) to determine if changes occur in the friability and structure of bract during postanthesis development and (B) to develop a tracer technique suitable for following the micronization of this plant part. Whole bracts were collected from greenhouse‐grown cotton, ‘Tamcot SP21’. Bract friability was determined by placing whole bracts in porcelain jars and abrading these plants with porcelain cylinders for ½‐hour on a roller mill. Whole anthesis bracts were broken apart to the extent that 6% of their weight was collected in a particle size fraction < 250 μm. By contrast, in bracts collected from 20 to 120 days postanthesis there was a trend toward a greater percent of the bract to be broken apart to a particle size of < 250 μm by the same procedure. Observation of tissue sections prepared from bracts showed that this change in friability was associated with an increased number of lignified bundle sheath parenchyma cells and tracheary elements in bract veins. Other anatomical changes accompanying bract senescence included significant decreases in epidermal, mesophyll, and lamina thickness at or shortly after the time of capsule dehiscence. Four fluorescent dyes and two fluorescent brightening agents were applied separately in aqueous solution to cotton bract and leaf trash. Colour Index Basic Yellow 37 was found to be the most suitable dyeing agent. Two‐ to 10‐μm diameter particles obtained from the pulverized remains of dyed bract were distinguished from undyed bract particles of the same size by observation with an epifluorescence microscope using a 334‐ to 365‐nm exciter beam at a magnification of 625 ✕. Significant differences in friability of dyed and undyed bract were not observed by roller mill tests. It is reasonable to conclude that these tracer procedures will identify the bract component in respirable cotton mill dust.