Relationship of Automotive Lead Particulates to Certain Consumer Crops
Discussions Follow E. A. Schuck and J. K . Locke Air Pollution Research Center, University of California, Riverside, Calif. 92502
Five crops were analyzed for their lead content-cauliflower, tomatoes, cabbage, strawberries, and valencia oranges. I n addition, the soil, water, and air in contact with these crops were analyzed for lead. The combined findings from the edible portion of four of these five crops strongly suggest that automotive lead particulates are not absorbed. They exist rather as a topical dust coating of which a t least 50% can be removed by simple water washing. Neither did these crops show any inclination to absorb lead oiu their root systems. Similar conclusions relative to the fifth crop, Le., strawberries, cannot be drawn except by analogy to the other crops. In spite of growing near heavily traveled highways, Le., up to 50,000 vehicles per day, the amount of lead associated with the five crops in an untreated state was never greater than 1 pg. of Pb per gram of fresh weight. The average Pb concentration for the entire crop areas studied was one or two orders of magnitude less than 1 pg. of Pb per gram of fresh weight.
L
ead in our environment has been the subject of many investigations. These have included studies of lead associated with soils (Tatsumoto and Patterson, 1963 ; Chow and Johnstone, 1965); lead in water (Poldervaart, 1955); lead in air (USPHS Publ., 1965; Kehoe, 1964); and lead associated with biological systems (Bagchi, et ul., 1940; Kehoe, 1940; Kehoe, 1961). The intent of many of these studies has been to determine the possible effect of man’s use of lead compounds o n his environment. I n this current study the emphasis is on the interaction of airborne automobile lead particules and consumer crops. This implies more than a knowledge of the concentration of lead found in crops. I t implies a knowledge of the environmental system which is important to crop growth. Thus, without additional details, the analysis of crops in terms of their lead content leaves many unanswered questions. One major question is: How is the lead associated with the crop? Is it absorbed, and if so, is it absorbed oiu the surface of the plant or is it absorbed via the root system? Assuming lead is found associated with consumer crops, what is the source of that lead? Many soils normally contain lead and past agricultural practices may have increased these lead levels. Therefore, knowledge must be generated concerning the lead found in the air, the water, and the soil, in addition to that found associated with the crops. 324 Environmental Science & Technology
Experimental The success of a research plan depends in most cases on the development and maintenance of specialized analytical skills. This is particularly true in this present study which required accurate determination of small amounts of lead found in a variety of materials. The method used was the colorimetric dithizone technique. Technical personnel associated with this project were trained in this latter technique at the Air and Industrial Hygiene Laboratories of the California State Department of Public Health in Berkeley, Calif. I n addition to this specialized training, a continuous program of cross checking with other laboratories was established. Participating groups in addition to the California Public Health Agency were the Ethyl Corporation in Detroit, Mich., and American Smelting and Refining in Salt Lake City, Utah. I n all cases reported herein, the terms washed or unwashed refer to simple water washing such as might be used in the preparation of food in the home. Unless otherwise specified, the Pb content of a given edible crop refers to a n aliquot taken from a blended sample containing one or more of the fruit or vegetable items being analyzed. The soil analysis is restricted to that portion of the lead which is soluble in 10% nitric acid during a three-day contact time. Particulate air samples were collected on 2-inch Gelman Triacetate Metricel filters having a 0.8-p pore size. All air samples were collected at a point 18 inches above the ground with the filter holder facing down. Pb concentrations relating t o crops are reported in terms of fresh weight. Although not reported herein, the crops were also analyzed in a dried state. The fresh cs. dry values are completely comparable, providing the original moisture content of the crop is known. With the exception of the airborne particulate samples, the concentrations are given in units of pg. of lead per g. of material analyzed (pg. P b per g.). One pg. Pb per g. is equivalent to one part per million (1 p.p.m.) by weight. Airborne particulate concentrations are reported as pg. of lead per cubic meter of air (pg. Pb per m. One pg. Pb per p.p.m. P b by weight. m. is equivalent to 8.5 X The area chosen for investigation of a cauliflower crop was immediately adjacent to and downwind from a highway with an average daily vehicle count of 58,000. Samples of ripe cauliflower were collected at 42 arbitrary grid points in this 10-acre plot. Table I contains the results of lead analysis of the edible portion of these collected flowers at the 42 sampling points, Interior edible portions of the flower were also analyzed. These portions were collected by cutting into the base of duplicate flowers collected at the same 42 sample sites. The ”>.
Table I. Pb Content of Fresh Cauliflower pg. Pb per g. of Cauliflower Distance from Highway (ft.1 50 250 450 650 850 1050 1195 A
‘J B
= =
_
_
Aa 0.25 0.16 0.00 0.01 0.00 0.00 0.00
0
~
-
Bh 0 00 0.00 0.00 0.00 0.00 0.00 0.00
,
70
Ae 1.02 0.32 0.00 0.00 0.04 0.00 0.00
Distance Along Highway 197 . Bh An Bh 0.00 0 . 2 0 0.00 0 . 0 5 0 00 0.00 0.00 0.00 0 . 0 0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
(ft.) ~~
272
134
Bh 0.11 0.35 0.02 0.35 0.00 0.00 0.00
Aa 0.23 0.02 0.08 0.00 0.00 0.00
362 Bh 0 00 0.00 0.17 0.07 0.00 0.00 0.00
A(z
0.13 0.00 0.11 0.04 0.00 0.00 0.00
Aa 0.16 0.01 0.13 0.00 0.00 0.00 0.00
~-
Bh 0.05 0.16 0.00 0.00 0.00 0.00 0.00
_ ~Average ______
Aa 0.33 0.11 0.04 0.02 0.00 0.00 0.00
Bb
0.03 0.09 0.03 0.07 0.00 0.00 0.00
average \ d u e for entire flower. average \ d u e for interior portions of flower.
Table 11. Pb Content of Soil in Cauliflower Field pg. Pb per g. of Dry Soil Distance Along Highway (ft.) 134 197
70
50 250 450 650 850 1050 1195 h
A B
= =
107 97 75 93 69 102 115
3.2 0.005 0.005
151 92 64 67 95 90 68
2.0 0.005
91 82 79 95 71 68 89
0.6 0.3 1.2
