LITMIR.BIZ

Figure 6.2 Irradiation of sample pellets using compact energy dispersive X‐ray fluorescence (EDXRF) system.

      6.2.6 Accuracy and Precision of the Method

      6.2.6.1 Construction of Calibration Curve

In any analytical technique, validation of the method is the most important quality control issue. Accurate and precise results depend on the careful construction of the method or analytical technique which produces them. A calibration curve was constructed using three lab‐synthesized secondary standards of arsenic in varying concentrations (5.8, 9.5, and 14.8 ppm) prepared from commercially available 1000 ppm As standard (Mark, Germany). The secondary standards were prepared by doping 2 g of cellulose with different amount of As [7]. The accurate concentrations of the element in the standards was obtained by the source excited by EDXRF. Figure 6.3 shows the calibration plot of As reflecting a good regression value. A certified reference material (CRM) Orchard Leaf (NIST 1571) obtained from the US‐based National Institute of Standards & Technology, was prepared and analyzed under same condition as the real samples and used to check the accuracy and precision of the analytical method [8]. The calculated values of relative error (%) and variation (%) as shown in Table 6.1. was found in good agreement with the certified values and within an error margin of 10%, thus confirming the method is quite fit for purpose.

      6.2.6.2 Measured Condition

6.3 Determination of Lead Concentrations in Human Whole Blood Using EDXRF Technique with Special Emphasis on Evaluating Association of Blood Lead Levels with Autism Spectrum Disorders (ASD)

      6.3.1 Background

Autism spectrum disorders is an emerging and increasingly relevant point of social concern. ASD is a range of potentially devastating childhood conditions associated with environmental, genetic, and epigenetic factors. Some of these effects appear to be transgenerational. ASD is a kind of neurodevelopment disorder that can produce features such as impaired psychosocial and adaptive skills functioning, as well as lack of social interaction, poor communication skills, and compulsive patterns of activity [9] are also reported regarding ASD. It is thought that autism is initiated by disruption of normal neurobiological mechanisms during the prenatal period, accompanied by strong genetic components, but nongenetic factors are likely involved as well with increased prevalence.

      A combination of genetic susceptibility and exposure to environmental toxins at critical periods during brain development has recently been hypothesized as the origin of autism [10] and several studies have observed elevated levels of heavy metals and essential minerals among children diagnosed with ASD [9]. Johnson and Myers [11] suggested that environmental exposure to heavy metals and essential minerals may act as a central nervous system teratogen in early gestational life. Among the toxic heavy metals, Pb is of particular concern as an undesirable contaminant originating from a variety of common sources such as motor vehicles, lead paint, contaminated soil etc. Pb can be ingested through air, drinking water, food etc. Developing fetuses and children are more sensitive to Pb exposure compared to adults because of the relative immaturity of the blood–brain barrier, increased gastrointestinal absorption, and the prevalence of hand‐to‐mouth behaviors. Hence the possibility of Pb exposure leading to the development of ASD in children is of greater concern to children than adults.

      Many studies from across the world support the association between exposure to Pb and ASD. But different, conflicting [12] opinions are also available and must be taken into consideration. Adams et al. [13] conducted a study where they compared 55 children with autism ages 5–16 years to 44 control subjects of similar age and gender and reported that the autism group had significantly higher levels of Pb in their red blood cells and higher urinary levels of lead,

Скачать книгу