Detection of inorganic micropollutants in waters - future development of analytical techniques
The development of analytical techniques is, for the most part, linked to the emergence of new standards concerning the environment or drinking water. As regards inorganic micropollutants, particular attention has been focussed in the recent past on determining the forms in which these elements were to be found in water. This approach has not been adopted, however, in all of the standards proposed since then. In all of these standards the analyte of concern is the total undifferentiated element. Methods of determining trace element speciation would therefore no longer appear to be the order of the day. In fact this is not so, for given that the limits set are increasingly low, a knowledge of the forms and valencies in which these elements are to be found is more and more important for optimisation of the treatment processes designed to remove these inorganic micropollutants. Such is the case, for example, with iron, arsenic, selenium and chromium. Arsenic, for instance can only be properly eliminated if found in the +V oxidation state; prior oxidation may therefore be necessary. In the case of chromium, the reverse is true, since the element in question cannot be eliminated if present in oxidation state +VI. It has therefore to be reduced to bring it to the +III oxidation state. A further development in analysis concerns the possibilities offered by IPC-MS couplings. Indeed, knowledge of the isotopic ratios as regards a particular element can be essential in discovering the origin of a pollution episode. Two cases are presented here : 1. A heavy element, which undergoes little or no isotopic segregation, as in the case of lead. - Investigations into high lead level in blood of children can reveal significant contamination (>150 mg Pb /l of blood). The origins of this lead can be multiple: atmospheric pollution (natural, automotive), old paint (dust), drinking water that has passed through lead pipes. Isotopic analysis alone allows one to identify the preponderant lead source: examples are given in the paper. 2. A light element, which would normally be subject to isotopic segregation, but which does not precipitate and which adsorbs very little or not at all. Such is the case with boron. - Boron can also have several origins. For example, in detergent products the boron comes for the most part from California and to a lesser extent from Turkey for the rest. This boron has a different isotopic signature from that of the boron found in France. This method enables us to distinguish boron used in agriculture, or natural boron, from the boron used in the formulations of cleaning products.