Trace Elements in Tears: Comparison of Rural and Urban Populations Using Particle Induced X-ray Emission

Abstract

We aimed to evaluate the types and concentrations of trace elements in tears of individuals living in urban and rural environments using particle induced X-ray emission (PIXE) and the possible association with exposure to air pollution and suggest a novel method for tear-based biomonitoring studies. This cross-sectional pilot study comprised 42 healthy subjects, 28 living in a rural area and 14 in an industrial city. Tears were collected with Schirmer paper and characterized by PIXE. Trace element concentrations from both eyes were averaged together with environmental pollution data. Main outcome measures were between-group differences in types and concentrations of trace elements in tears and comparison to environmental data. The rural group included 12/28 men, mean age 45.2 ± 14.8 years. The urban group consisted of 11/14 men of mean age 27 ± 5.9 years. Six rural and all urban were active smokers. Air pollution data showed more toxic elements in the rural environment. On PIXE analysis, chlorine, sodium, and potassium were found in similar concentrations in all samples. Normalizing to chlorine yielded higher values of aluminum, iron, copper, and titanium in the rural group; aluminum was found only in the rural group. The higher levels of certain trace elements in the rural group may, in part, be a consequence of exposure to specific environmental conditions. No direct association was found with air pollution data. PIXE is useful to analyze trace elements in tears, which might serve as a marker for individual exposure to environmental pollutants in biomonitoring studies.

Tear Fluid as a Matrix for Biomonitoring Environmental and Chemical Exposures

“…Nonetheless, tear uid demonstrated the capacity to identify difference in exposure groups. For example, signi cantly elevated concentrations of elemental iron, copper, and chromium was found in the tear uid of the rural group compared to urban group (p < 0.05) 58 . Aluminum was only identi ed in the tear uid of rural participants but not urban participants 58 .…”

“…For example, signi cantly elevated concentrations of elemental iron, copper, and chromium was found in the tear uid of the rural group compared to urban group (p < 0.05) 58 . Aluminum was only identi ed in the tear uid of rural participants but not urban participants 58 . The comparison of rural and urban groups is intriguing because rural groups have been traditionally underrepresented in exposure research 59 despite being at high risk for exposure to pesticides 60 and metals 61 .…”

“…Tear uid analysis has revealed. Elevated levels of titanium were found in in tear samples of individuals who worked with pesticides 58 while tear uid of shipyard welders had a signi cantly higher lead concentrations compared to a group of healthy controls (p = 0.016) 62 . Occupational exposure to lead has been well-documented in welders using blood-based biomonitoring 63 .…”

“…Human biomonitoring of trace metals utilizing hair and nails is well established; however, variables such as hair and nail length, lack of characterization for some elements, and personal product use (e.g., shampoo, nail polish) may impose limitations 56,57 . Trace metal concentrations in the tear uid have been used to compare rural and urban exposure to air pollution, and to correlate air pollution levels with trace metal concentrations in the tear uid 58 . Although no correlation was found between tear uid trace metal concentrations and air quality (p > 0.05), this may be due to the multiple sources of exposure (e.g., smoking status, occupation) 58 .…”

“…Trace metal concentrations in the tear uid have been used to compare rural and urban exposure to air pollution, and to correlate air pollution levels with trace metal concentrations in the tear uid 58 . Although no correlation was found between tear uid trace metal concentrations and air quality (p > 0.05), this may be due to the multiple sources of exposure (e.g., smoking status, occupation) 58 . Nonetheless, tear uid demonstrated the capacity to identify difference in exposure groups.…”