In line with recent European environmental guidelines on biomasses, one of the most important parameters to take into account is the As concentration, especially when present in biomasses and complex matrices. The goal of the present study is to give information about possible technical-analytical problems during the determinations of such elements by means of different instrumental spectroscopy techniques, in particular inductively coupled plasma atomic emission (ICP-AES) and atomic absorption (AAS), using two different wavelengths, 188.98 nm and 193.70 nm. In the Laboratory of Hygiene of National Institute of Health in Italy, a specific study has been carried out concerning the determination of As contents in environmental solid matrices, using as reference material BCR 141 R, represented by a calcareous soil. In particular, whereas recovery tests did not show particular drawbacks, difficulties were met in the As detection in reference material. Spectral interference was seen during determination by ICP-AES and matrix interference during determination by AAS, in particular using ETAAS with deuterium background correction and HAAS. Using ETAAS with Zeeman background correction at 193.70 nm, the As line did not show particular matrix interference during the reading of samples.A ring test involving two more laboratories and another certified reference material (IAEA-356 in marine sediment matrix) produced important information about problems of under/over estimation of data. Two different instrumental techniques, ICP-MS and HAAS, confirmed previous data, i.e., overestimation for inductively coupled plasma mass spectrometry and that As values achieved by HAAS were of the same order as the references, but affected by considerable standard deviation. In the light of this study, data achieved on the environmental matrices investigated suggest that the critical step in As determination is the instrumental reading, rather than the mineralization process. Further, each of the methods proposed, apart from ETAAS with Zeeman background correction, presents its own peculiar drawbacks and no particular advantage over other techniques.