The rapid decomposition of biological materials by using a microwave acid digestion bomb.

A microwave acid decomposition technique was evaluated for decomposing biological standard reference materials (NBS oyster tissue and bovine liver) for trace metal analyses. Dissolution consisted of HNO3 decomposition in a closed Teflon bomb. A microwave oven was used as the heat source. Complete decomposition times were less than 1 min. Resulting solutions were analyzed by atomic absorption spectrophotometry for Cd, Cu, Fe, Pb, and Zn. Recoveries were estimated by comparison with National Bureau of Standards certified values. The precision and accuracy of the results ranged from 1 to 13% and 93 to 106%, respectively.

Threat to the New York City water supply--plutonium.

The mayor of the City of New York received an anonymous letter on April 1st 1985 threatening to contaminate the water supply with plutonium unless all criminal charges against Mr Bernhard Goetz, the suspect in a dramatic subway shooting incident, were dismissed by April 11th 1985. Local and Federal authorities were called upon to evaluate the credibility of the threat and to institute a "round the clock" monitoring program by New York City personnel. The Environmental Measurements Laboratory, EML, was requested by the City to analyse a composite, large volume (approximately 175 litres) drinking water sample collected by City personnel on April 16th 1985. The concentration measured was 21 fCi/l which was a factor of 100 greater than previously observed results in our data base, and the mass isotopic content of the plutonium was very unusual. Additional samples were collected one to three months later at various distribution points in the water supply system. The plutonium concentrations were much lower and comparable to EML's earlier data. Mass isotopic analysis of these samples provided more reasonable compositions but with high uncertainties due to very low plutonium concentration. Recent measurements of large volume samples, approximately 1000 litres, collected in the Fall of 1985 from the New York City and New Jersey water supplies showed identical plutonium concentrations of 0.05 fCi/l. Mass isotopic analyses indicated similar 240Pu/239Pu ratios which were slightly lower than global fallout estimates. Due to our inability to confirm the elevated plutonium concentration value for the composite sample of April 16th 1985, it is impossible to conclude whether the threat to contaminate the New York City water supply was actually carried out or whether the sample was contaminated prior to receipt at EML.

Electrothermal atomic-absorption spectrometric analysis of lake waters for Mn, Fe, Pb and Cd.

Analyses have been made for trace metals in surface waters from lakes known to be sensitive to inputs of acidic deposition. Electrothermal atomic-absorption spectrometry was used for direct measurement of the low metal concentrations. The studies revealed non-spectral interferences resulting from small amounts of inorganic material in the sample matrix that prevent accurate measurements of Mn and Pb. Several types of interferences were identified by means of a computer coupled to the atomic-absorption spectrometer and procedures to overcome them were evaluated. Matrix modification with nitric acid is required for the determination of Mn. Atomization from a platform inserted within the graphite tube is necessary for interference-free Pb determination.