The biokinetics of thorium nitrate after deposition in the rat lung: implications for occupational exposure

Biokinetic studies in rats have indicated that: 1) thorium nitrate behaves more like a Class Y compound than a Class W compound as defined by ICRP; 2) any increased excretion of thorium in the presence of excessive amounts of Class D uranium compounds does little to arrest the substantial reduction in the ALI from that based on uranium alone; 3) the behaviour of thorium is sufficiently different from that of its gamma-ray emitting daughter radionuclides as to cast doubt on the reliability of external monitoring techniques for assessing intake; and 4) the chelating agent DTPA will be of little value for treating workers overexposed to thorium. (Author)