Application of Fourier-transformed-infrared spectroscopy to quantitate amorphous silica in personal air samples in sugarcane cutters

Abstract

In recent years, chronic kidney disease of unknown origin (CKDu) has risen to an epidemic level in Latin America. Specifically, in agricultural communities of sugarcane cutters, the burden of the disease is unusually high. Several hypotheses exist as to the cause of the disease, focusing on various risk factors, including dehydration, nutrition, and thermal stress. Another important risk factor warranting further research is exposure to particulate matter (PM), given its nephrotoxic potential. PM can be defined as solid or liquid particles present in the environment, often microscopic. Sugarcane workers are exposed to high PM concentrations containing various contaminants, including amorphous silica. In sugarcane, the leaves and other excess plant material contain amorphous silica that can be released into the worker's environment during harvest. Quantitating this amorphous silica and determining if it can play a deleterious role in kidney health has become a priority. Still, amorphous silica is a challenging analyte that requires time- and cost-intensive analysis. A previous pilot project aimed to develop a predictive model using Fourier-Transformed-Infrared Spectroscopy (FTIR) to analyze amorphous silica non-destructively and cost-effectively compared to the currently accepted NIOSH method (e.g., X-ray diffraction). The model was created, and initial concentrations of amorphous silica were determined. During the analysis of samples, the need to ascertain the detection limit of the FTIR method was evident. This project, therefore, further aimed to evaluate and analyze amorphous silica using direct-on-filter FTIR spectroscopy. The point of analysis where several discrepancies occurred (i.e., inconsistency with detecting the peak, loading amounts detected, etc.) was determined to be approximately 500 micrograms before the FTIR began to over or underestimate the absorbance values based on concentration changes. This study is one of the first attempts to use FTIR to non-destructively analyze and quantitate air sampling filters. Additionally, the results will be compared to the current limit of detection values for the FTIR methods employed by NIOSH for their silica analysis tool, further contributing to the literature.