Reference levels and relationships of nine elements in first-spot morning urine and 24-h urine from 210 Chinese children

Toxic elements have caused great concern due to their adverse health effects. Biological monitoring is generally considered to be a useful tool to assess human exposure to these elements during risk assessment. To better interpret the biological monitoring data, elemental reference values are critical. The major objectives of this study were to clarify whether first-spot morning urine can serve as a surrogate for 24-h urine and to determine the concentration reference interval of some elements in Chinese children's urine. In total, 259 first-spot morning urine samples and 24-h urine samples were collected from 210 2- to 12-year-old healthy children in China and analyzed for creatinine, aluminum, barium, manganese, titanium, cerium, scandium, vanadium, yttrium, and arsenic. The results showed that the creatinine-adjusted concentrations of aluminum, barium, manganese, titanium, cerium, scandium, vanadium, yttrium, and arsenic in the first-spot urine were significantly correlated with those in the 24-h urine. This showed that first-spot morning urine is a favored matrix for monitoring element exposure due to its easy collection and low collection cost. The reference interval using ng/mg creatinine as the unit for Chinese children's urine was 1.63-2653 for aluminum, 3.71-116.8 for barium, 0.67-91.77 for titanium, 0.20-53.42 for arsenic, 1.36-25.29 for manganese, 0.24-8.59 for vanadium, 0.02-2.27 for cerium, 0.01-0.65 for yttrium, and 0.002-0.483 for scandium. These reference intervals may provide reference levels to assess Chinese children's exposure to these elements.