Mineralogy and granulometry of settled dust in a dust-dune-loess-liquid waste system in the northern Negev Desert, Israel

Abstract

Settled dust mineralogy and granulometry of the Negev semi-arid desert were examined in samples collected at 1 and 3 m above ground level over a period of 5 years. Evaporation ponds which are designed to collect industrial waste, overflow and contaminate the loess in which they are built and the dust that settled around them. Some of this dust is incorporated in new loess, and some dust continues its transport to new locations, carrying the contaminants with it. Kaolinite and calcite particles in the dust deposits were found to serve as hosts to grains of quarts, pollen, and stamen that were much smaller in diameter and were tightly attached to the surfaces of the particles. The median diameters of the particles at both levels varied between 4 and 50 μm, and the coarsest diameters approached 150 μm. Most of the finest five percentile fraction, during 4 of the 5 years, were below 4 μm in diameter at both levels. These particles are small enough to enter the alveoli of our lungs. Modal triangle analyses show that the loess is better sorted in relation to the local dust, and it is coarser grained. It is suggested that the local winds may supply coarse particles at ground level, and light rainy events may remove, by suspension, some of the finer particles, thus converting the constitution of the local dust deposits into the highly porous structure of loess; thus creating a potential trap for a large volume of liquid industrial waste. Lognormal distribution of the same samples shows variation from non-lognormalcy in the dust, to ∼ 100% lognormalcy in the loess. Two major constituents, quartz and calcite, dominate in all the samples, but finer grained dust populations are richer in calcite vs. quartz than coarser populations. Dust east of the monitoring station is different from that west of it, as is the geology in the corresponding areas. The several industrial plants east of the dust monitoring station also contribute to the elemental dust composition.