Analytica Chimica Acta 569 (2006) 221–226 Paired emitter-detector light emitting diodes for the measurement of lead(II) and cadmium(II) King-Tong Lau * , Eimear McHugh, Susan Baldwin, Dermot Diamond * Adaptive Sensors Group, National Centre for Sensor Research, School of Chemical Sciences, Dublin City University, Dublin 9, Ireland Received 8 December 2005; received in revised form 13 March 2006; accepted 20 March 2006 Available online 29 March 2006 Abstract A transmittance mode optical device based on using a reverse biased light emitting diode (LED) as light detector has been developed for colorimetric analysis. This new optical device was validated with bromocresol green dye for absorbance measurements before being employed for detecting cadmium(II) and lead(II) in water. Results show that the performance of this LED-based device is comparable to much more expensive bench top UV–vis instruments, but with the advantages of being low cost, low power and simple to operate. © 2006 Elsevier B.V. All rights reserved. Keywords: Paired light emitting diode (LED) detector; Cadmium(II); Lead(II); Colorimetric analysis; Optical sensing; Environmental monitoring 1. Introduction Heavy metals are dangerous because they tend to bioaccumu- late. They can enter a water supply by industrial and consumer waste, or even from acidic rain breaking down soils and releasing heavy metals into streams, lakes, rivers, and groundwater. Lead in the environment arises from both natural and anthro- pogenic sources. Consumer electronics constitute 40% of lead found in landfills. The main concern in regard to the presence of lead in landfills is the potential for the lead to leach and contaminate drinking water supplies. Lead accumulates in the environment and has high acute and chronic toxic effects on plants, animals and microorganisms. People, animals, and fish are mainly exposed to lead by breathing and ingesting it in food, water, soil, or dust. The major source of lead intake for humans is from food. Other sources such as water in areas with lead piping, air near point of source emissions, or contaminated land are also impor- tant. Exposure to lead can result in a wide range of biological effects depending on the level and duration of exposure. Lead accumulates in the blood, bones, muscles, and fat. Infants and young children are especially sensitive to even low levels of lead, * Corresponding authors. E-mail addresses: kim.lau@dcu.ie (K.-T. Lau), Dermot.diamond@dcu.ie (D. Diamond). which causes damage to the kidneys, liver, brain and nerves, and other organs. High levels of exposure may result in toxic bio- chemical effects in humans which in turn cause problems in the synthesis of haemoglobin, effects on the kidneys, gastrointesti- nal tract, joints and reproductive system, and acute or chronic damage to the nervous system [1]. Average daily lead intake for adults is estimated at 1.6 g from air, 20 g from drinking water and 28 g from food. The World Health Organisation (WHO) and the U.S. Environmental Protection Agency (EPA) tolerate a maximum of 50 ppb of lead in drinking water [2,3]. Wild and domestic animals can ingest lead while grazing. They experience the same kind of effects as people who are exposed to lead. Low concentrations of lead can slow down veg- etation growth near industrial facilities. Lead can enter water systems through runoff and from sewage and industrial waste streams. Elevated levels of lead in the water can cause repro- ductive damage in some aquatic life and cause blood and neu- rological changes in fish and other animals that live there. Cadmium derives its toxicological properties from its chem- ical similarity to zinc, an essential micronutrient for plants, ani- mals and humans. Cadmium is biopersistent, once absorbed by an organism, remains resident for many years. Long-term expo- sure is associated with renal disfunction and bone defects (osteo- malacia, osteoporosis) in humans and animals. High exposure (above the EU maximum admissible concentrations (MAC), which is 5 ppb in drinking water) can lead to nausea, vomiting, diarrhoea, muscle cramps, liver injury; exposure to contami- 0003-2670/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2006.03.073