Aerial Deposition Research Articles

A study of heavy metal contamination in the Rhondda Fawr, South Wales

Analysis of vegetation and soils of the Rhondda Fawr, South Wales, shows that there is contamination by the heavy metals Pb, Cd, Cu and Ni throughout the valley, in particular within the urban development area. It is suggested that this contamination occurs mainly by aerial deposition, and that in the case of Pb, Cd and Ni the motor vehicle is the primary source.

Rates and Routes of Transport of PCBs in the Environment

Polychlorinated biphenyls (PCBs) are one member of a class of chlorinated organic compounds which give rise to concern, because of their wide dispersal and persistence in the environment and tendency to accumulate in food chains, with possible adverse effects on animals at the top of the food webs, including man. In the past, attention has been concentrated on chlorinated hydrocarbon pesticides, such as DDT, dieldrin, heptachlor and HCH (hexachlorocyclohexane). More recently attention has been focused on PCBs and on chlorinated dibenzodioxins. Likely candidates for future attention are hexachlorobenzene, chlorinated dibenzofurans, and chlorinated phenols. In the past, such compounds have generally been studied individually. As the number of compounds giving rise to concern increases, there is an urgent need to establish uniform monitoring schemes and generalized models describing environmental transport and bioaccumulation which will be applicable to all compounds with these properties. Models such as the global monitoring scheme outlined by the SCEP study (1), and the global transport model outlined recently by Woodwell et al. (2), are needed in order to help identify sources of environmental contamination, to establish acceptable levels of discharge, and to estimate the effectiveness of different control strategies. This paper summarizes the fragmentary knowledge available about production, uses, and losses of PCBs, and attempts to define the major routes of transport and reservoirs of PCBs in the environ-

Rates and Routes of Transport of PCBs in the Environment

Rates and Routes of Transport of PCBs in the Environment

The Dye-Tracer Method for Measuring Aerial Spray Deposits in Forest Insect Research1

The dye-tracer method for measuring aerial spray deposits consists of dissolving a known amount of dye in the spray liquid and then measuring the amount of dye recovered in the spray deposit. In forest insect research dye tracers are used for studying the spray distribution from various types of aerial spray equipment and aircraft, and for evaluating spray coverage on small forest plots. At the time of spraying, deposit samples are taken on glass or metal plates. Then, in the laboratory, the deposits are washed of (and the dye in each is measured in a Dubosq® colorimeter or a spectrophotometer. Of the two, the colorimeter is faster but has a lower sensitivity (0.05 gallon per acre). The spectrophotometer procedure, while more complicated, has a sensitivity of 0.02 gallon per acre and in addition will measure each of the 2 dyes in the mixed deposit from the dual-sprayer apparatus.

Spread Factor Variation for Oil-Base, Aerial Sprays

Aerial spray deposits are commonly assessed by collecting samples of either undyed spray on oil-sensitive dyed paper cards or dyed spray on undyed cards. Since the spread of oil-base spray drops changes disproportionately with drop size, the spots on the cards must be converted back to the original (spherical) drop sizes. This is accomplished by dividing the spot diameter as measured on the card by a suitable spread factor. A procedure is presented for determining this spread factor. Variation of the spread factor with drop size, sampling surface. and different sprays is discussed. The spread factor increases with increasing drop sizes regardless of the kind of assessment paper and spray. The rate of this increase depends primarily on the kind and source of spray materials used in the formulation. Therefore, for an accurate spray deposit assessment, the spread factor should be determined for a range of drop sizes for each different spray formulation.