The Laboratory for Membrane Chemistry (LMC) of the National Institute of Advanced Industrial Science and Technology (AIST), an independent administrative institution, has succeeded in developing a simple lead-detecting method based on enrichment with membrane followed by visual detection. The simple detecting technique is expected to provide an on-site and low cost means of monitoring trace lead ion in environmental water and industrial waste.

Lead is harmful heavy metal giving fatal damages to brain and nerve, with industrial waste standard set at 100 ppb, and environmental and drink water standards at 10 ppb. The World Health Organization (WHO) recommends the environmental standard of lead to be 10 ppb, and the Restriction of Hazardous Substances in Electrical and Electronic Equipment (RoHS) Directive of EU puts restrictions on the use of lead.

The LMC-AIST developed an innovative method of determining trace concentration of lead in water, consisting of separation and concentration of lead by filtering a sample solution with a filter made of compressed cerium phosphate fibers and assessment of lead ion concentration through a simple visual colorimetry based on the reaction of concentrated lead ion with coloring reagent (Fig. 1).

The simple measuring method has merit of detecting lead ion at a concentration much lower than the water quality standard, which can be achieved by an unskilled person on the spot and at a low cost. The technique will be spread as a simple mean for making on-site monitoring of environmental water and drink water, and in developing countries where sophisticated analytic equipment is not available. Further efforts will be paid to the commercialization of the system in collaboration of enterprises dealing with simple measuring instruments and filtering membrane.

Fig. 1. Detection of trace level lead through concentration and coloration

It has been known that when the human body is exposed to lead for a long period, fatal damages may occur in the brain and nerves. The WHO is recommending an environmental quality standard as strict as 10 ppb. The quality standards for environmental water and drink water in Japan are also adopted to 10 ppb. In addition to industrial pollution of environmental water, contamination of drinking water with lead dissolved out of city water piping is coming to a serious issue. For monitoring trace lead around 10 ppb, however, the analysis with a large-sized analytical instrument has been needed up to now. Under such a circumstance, it is urgently required to develop a simple multi-purpose method for determining trace contents of lead in mining and industrial wastes, river water and city water, which can be carried out by an unskilled person wherever monitoring is needed. At present, none of simple methods is available for determining lead at a high sensitivity in compliance with the water quality standard.

The LMC-AIST has noticed the need of pretreatment for the determination of trace level (ppb) lead ion, involving isolation and concentration. On the basis of a finding that fibrous crystals of cerium phosphate selectively react with lead ion, it has been attempted to compress fibrous crystals to make a sheet of filtering membrane. Passing sample water through this filter proved to condense lead ion. Additionally, it has been found that coloring reaction of lead ion with certain test reagent makes it possible visually assess lead concentration at a trace level. The combination of isolation-concentration of lead ion with visual assessment based on coloring reaction will provide a simple means for monitoring trace lead on the spot.

The simple method of detecting lead ion proposed here consists of isolation and enrichment of lead ion through the selective adsorption of lead ion with a filter made of fibrous crystals compressed into a membrane, and coloring reaction with certain reagent to assess lead content through visual means. The filter is prepared by compressing fibrous crystals of cerium phosphate alone or in combination with cellulose fibers into a sheet. The detection sensitivity may be upgraded by increasing the volume of sample water. If 100 ml sample water is used, the sensitivity can be improved to 5 ppb.