Simple digestion procedure followed by the azomethine-H method for accurate boron analysis and discrimination between its fractions in wastewater and soils.

Excess boron is a growing environmental problem. It often affects agricultural yields, where reuse of wastewater for irrigation is practiced. This problem raises the need for reliable, simple and economical methods to monitor boron concentrations in wastewater and soil extracts. One such method, the commonly used azomethine-H spectrophotometric method, suffers from color interference, originating from high concentrations of dissolved organic matter, when applied to many wastewater and agricultural soil extracts. Moreover, this method only quantifies free dissolved boron and lacks the ability to quantify boron that is adsorbed to either the dissolved organic matter or suspended solids that are present in the sample. This work suggests a modification of the standard azomethine-H method, in which the solution is digested with potassium persulfate prior to the standard procedure. We show that this pretreatment can overcome the color interference and lead to highly accurate and precise boron analyses in wastewater. In soil extracts, the boron concentrations obtained using the suggested procedure were better correlated to inductively coupled plasma (ICP) spectrometry results than those measured by the standard method, because whereas the standard method quantifies the free dissolved boron only, the modified method, like the ICP method, quantifies the total dissolved boron in the sample. Thus, the suggested modification can be used to quantify the respective distributions of free dissolved boron, boron adsorbed to dissolved organic matter and boron adsorbed to suspended solids in soil extracts and water samples.

Heavy metal accumulation by Nicotiana glauca Graham in a solid waste disposal site.

Nicotiana glauca Graham, is the only perennial shrub growing in a solid waste contaminated site in the Negev desert of Israel. The concentration of heavy metals (Cu, Fe, Mn, Zn, Ni, Cd and Pb) in the upper soil layer was significantly higher (p<0.01) than in non-contaminated desert soil. In root and shoot of N. glauca, growing in the site, the concentration of Cu, Zn and Fe was significantly higher (p<0.05) than in plants of a non-contaminated site. In a controlled experiment, the concentrations of Zn and Cu in root of plants grown, in a mixture of contaminated and non-contaminated soil (1:1) was 9.5 and 4.7 higher than that of plants grown in non-contaminated soil, respectively. While Zn was accumulated in shoot of plants grown in contaminated soil (531 mgkg(-1)) in significantly higher concentration than in plants grown in non-contaminated soil (56 mgkg(-1)), no significant differences were found in Cu accumulation. Growth of N. glauca was inhibited on contaminated soil, but no other obvious stress symptoms were apparent. Therefore, long term experiments under controlled conditions are planned to study the mechanism of heavy metal tolerance and accumulation in N. glauca.