Figure 3.Nyquist diagram showing the namely influence of temperature and contamination in the impedance.It is concluded from the electrochemical studies and patents of impedance measurements of lubrication oils [29�C34] and the Nyquist plots that low frequencies are the most sensitive to variations in impedance due to changes of the dielectric constant of the fluid. However, the shortcoming of performing low frequency impedance measurements is that small deviations of the measurement frequency lead also to great changes in impedance. Yet, high frequency impedance measurements provide similar readings of impedance at the vicinities of the no
Environmental pollution by xenobiotics is increasingly becoming a global issue.
In connection with the growing ecosystem contamination by xenobiotics, it is therefore increasingly important to monitor their presence and promptly assess potential risks to humans [1]. The United Nations Environment Programme (UNEP) aims at monitoring and removing cadmium from the environment [2]. Over the last 15 years The Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) has permanently listed Cd as No. 7 (out of 275 species) in its priority list of hazardous materials [3]. Cadmium��s fate in the environment is shown in Scheme 1. Cadmium in its elemental form is a soft, silver-white metal, which occurs with other elements in the Earth��s crust with average content of 0.13�C0.2 g t?1 in the lithosphere. This element is naturally found in air, water resources and soil as complex oxides, sulphides, and carbonates in zinc, lead, and copper ores [4].
Mining of iron and zinc ores, the burning of fossil fuels, plastics, dyes or road transport constitute the main sources of environmental cadmium pollution, and therefore the routes whereby it can enter the human food chain [5]. In mining global cadmium production increased during the period from 1970 to 2004 from about 17,000 tonnes to about 22,000 tonnes. Over the last Brefeldin_A 15 years, global consumption has remained relatively constant, at around 20,000 tonnes. Improperly disposal of batteries is another source of cadmium pollution [6]. In the atmosphere cadmium is mainly emitted to the atmosphere in particulate form. From Tubacin FDA combustion sources, cadmium may, however, be emitted partly as elemental gaseous cadmium, but as it is cooled, this cadmium is also quickly bound to particulate matter, so atmospheric transport of cadmium is governed by aerosol (particle) transport mechanisms.Scheme 1.Cadmium pollution��transport and cycle. Adapted according to UNEP Lead and Cadmium activities.Quite extensive data sets of cadmium concentrations in the water column exist for specific locations in the world��s oceans and for different years over the last two to three decades.