S. S. Krishnan

Human hair as a pollutant dosimeter

Human hair has been proved to be a better dosimeter than even blood for tracing most of the heavy metal toxins when they penetrate the biosphere. The high precision of the neutron activation analysis (NAA) enabled researchers to elegantly differentiate between endogenous and exogenous contamination and to thoroughly study poisonings caused by these physiologically-unimportant elements. An extensive amount of bench-scale work has been accomplished in these laboratories to show the capacity of INAA to detect the presence of 10 nuclides (or more) with a precision of about 5%. The principal objective of the present study was to employ this assaying power and the tendency of scalp hair to uptake metals from aqueous solutions, to design an adsorption system which can easily be used by the waste-management people who are searching for a cost-effective technique to monitor and remove these pollutants from relatively large volumes of industrial effluents.

Leachability of toxic elements from solid wastes

We have examined the leachability of the toxic elements cadmium, arsenic, mercury, and selenium from solid wastes. The solid wastes studied are municipal incinerator ash, coal fly ash, hospital incinerator ash, raw sewage sludge, sewage incinerator bottom ash, and sewage incinerator lagoon ash (which is a combination of bottom and fly ashes). Cadmium displayed the greatest leachability in all waste types, with 76% leached from the municipal refuse incinerator ash. Although the sources of elements in the wastes are diverse, the leachability and hence the bioavailability in the incinerator ash appears mainly determined by the volatility of the element.

In vivo measurement of nitrogen by NAA

Nitrogen in the human body is measured in vivo using prompt neutron capture gamma-rays. The quantity of nitrogen can then be used as measured of protein. Data are presented on three groups of subjects; volunteers of different ages, those with liver ailments, and those on peritoneal dialysis. The data show that the nitrogen measurements given information (in accord with clinical findings) which is not given by indirect methods of estimating lean body mass.

Comparison of the determination of body calcium by in-vivo neutron activation analysis (IVNAA) and dual energy X-ray absorptiometry (DEXA)

The measurement of total body calcium is an important tool in the diagnosis and treatment of many diseases associated with bone. This measurement is done by IVNAA or DEXA. A knowledge of normal bone mineral mass for a given person, is necessary to determine whether or not a measured quantity is normal or low. The factors that determine bone mineral mass in a person are not clearly known. IVNAA indicates that bone mineral mass is a function of height but not the age whereas the reverse is indicated by DEXA. In this work, we have measured the bone mineral mass of over 200 normal volunteers by IVNAA and DEXA and have developed a methametical model for DEXA (for lumbar spine and femoral neck) as a function of height, age, weight and years after menopause. In determining the bone mineral mass, height is the predominant factor under 20 years of age and age appers to be the dominant factor for over 20 years. The equation derived is useful in calculating the normal bone mineral mass in a patient against which the measured value can be compared.

In Vitro Accuracy and Reproducibility of Bone and Soft Tissue Measurements by DXA

Dual energy X-ray absorptiometry (DXA) is widely used for bone mineral measurements and is recently being used to measure soft tissue composition. In-vivo measurements are reproducible with excellent precision (1-2%) for bones and somewhat poorer precision for soft tissue composition. We have measured the bone mineral content (BMC), bone area and density (BMD, g/cm2) using aluminum plates of known weight and area in place of bone. In order to simulate tissue, cellulose (paper in the form of books) was used as the surrounding medium. Further experiments were done to determine whether the presence of thin bones would affect the results of soft tissue analysis.

Recent Developments in the Prompt-Gamma Total Body Nitrogen Measurement Facility of the Toronto General Hospital

The measurement of body nitrogen by neutron activation analysis provides a measure of protein status, using the constant numerical relationship of 6.25 between nitrogen and body protein. Measurements of nitrogen balance have been used routinely for studying changes of total body nitrogen (TBN). However, a method to measure total body protein (TBP), itself, is required to assess protein status of an individual, resulting from disease or from treatment. TBP has been clinically very useful in several studies, e.g. obesity following calorie restriction (Stallings et al., 1988), ascites following peritoneovenous shunting (Blendis et al., 1986), renal failure following the start of treatment by continuous ambulatory peritoneal dialysis (Schilling et al., 1985), cancer (Shike et al.. 1984) and (malabsorption following total parenteral nutrition (McNeill et al., 1982).

Studies of skeletal cadmium assay and toxicity

Flameless Atomic Absorption Spectrophotometry was found to be a sensitive (2·10−12 g detection limit), accurate but destructive method for cadmium assay in bone biopsy samples (about 30 mg dry weight). The inductively coupled plasma emission technique was poorer in sensitivity (1.2·10−9 g) and is also a destructive method. Activation Analysis is still less sensitive (2·10−8 g detection limit) but a nondestructive one. Cadmium was found to accumulate in bone of rats fed, for 5 weeks, 0, 50, and 100 mg Cd/l in drinking water and the bone concentrations were 0.16, 1.09, and 2.6 mg Cd/kg bone (dry wt). Histological examination of the bones showed that cadmium induced increased osteoid surface in the bone with no evidence of accompanying kidney damage. This suggests a primary effect of cadmium on bone rather than secondary effect due to kidney damage.

Clinical Studies on Osteoporosis

Osteoporosis is, by definition, a reduction in bone mass with remaining bone of normal composition. The related loss in bone strength results in fractures with little or no abnormal force. Since a valid measurement of low bone mass or osteopenia was not widely available until recently, the diagnosis of osteoporosis was based on evidence of vertebral fractures, together with generalized osteopenia, based on the radiological assessment of spinal radiographs. A vertebral fracture causes partial or complete compression (anterior or mid-vertebral compression or loss in height of the full width of the vertebrae). In the absence of low bone mass, however, these vertebral deformities would not be considered osteoporotic fractures. A vertebral deformity without osteopenia may be attributed, for example, to an old traumatic fracture, to genetic anomaly or to such pathological bone disease as tumour. With aging, we observe an increasing incidence of mid-thoracic anterior wedge deformities without radiological evidence of osteopenia. These age related deformities are not considered by radiologists to be vertebral fractures and usually the radiographs are reported as normal or normal for age. The radiological assessment of osteopenia is subjective, however, and a quantitative measurement of bone mass is required to provide a more reliable estimate of the degree of osteopenia associated with vertebral deformities. In addition, the quantitative measurement of bone mass should detect significant osteopenia with increased risk of fracture in patients without vertebral deformity.

Impact of In-Vivo Neutron Activation and Related Techniques in the Understanding and Treatment of Bone Diseases of the Elderly

In-vivo neutron activation analysis (IVNAA) has been used in this laboratory, approximately for the past twenty years, to determine the bone status of humans. For this purpose, the total body calcium (TBCa) is assayed and that is indicative of the bone mineral concentration of the individual. We have effectively used this method to diagnose, understand and monitor the treatment of osteoporosis among elderly women, particularly in post-menopausal women. This paper summarizes the technique and our experience in dealing with osteoporosis.

Hot atom effect on the leachability of elements in solid waste

The effect of neutron irradiation on the leachability of elements in solid wastes comprising of coal fly ash, hospital and municipal incinerator ashes was studied. There was a marked increase in leachability in the neutron irradiated wastes compared to non-irradiated wastes especially for elements such as As, Cd, Co, Cr, Sm and Zn. For elements such as Fe and Sm there was no significant difference in the leachabilities in the irradiated and non-irradiated wastes. The possible causes of this scenario and implications are discussed.