Total arsenic measurements assessment regarding legal threshold demands more than
average and standard deviation approach. In this way, analytical measurement uncertainty
evaluation was conducted in order to comply with legal requirements and to allow the balance
of arsenic in both water and sediment compartments. A top-down approach for measurement
uncertainties was applied to evaluate arsenic concentrations in water and sediments from
Guarapiranga dam (São Paulo, Brazil). Laboratory quality control and arsenic interlaboratory
tests data were used in this approach to estimate the uncertainties associated with the
methodology.