Discussion
Relationship of Automotive Lead Particulates to Certain Consumer Crops Walter W. H e c k National Air Pollution Control Administration, Consumer Protection and Environmental Health Service, Public Health Service, US.Department of Health, Education and Welfare. On assignment from: Crops Research Division, Agricultural Research Service, U.S. Department of Agriculture, Raleigh, No. Carolina.
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chuck and Locke suggest that this study serves more as a guideline for further studies, rather than providing unequivocal answers. Their main objective was to examine possible interactions between airborne automotive lead particulates and consumer crops. They suggest that much of their data prove lead particulates are deposited, but not absorbed by the five crops studied. Schuck and Locke stress the need for a detailed knowledge of the environmental system that carries the airborne lead particulates before one can determine the source of lead or the potential for lead uptake. This detailed knowledge was not always obtained nor, when obtained, always fully used. The authors stress the difficulties in analyzing for small amounts of lead, but on several occasions they suggest contamination as a reason for high values with no suggestion of analytical problems. In their section on experimental methods they indicate that crop lead values were obtained using an aliquot from a blended sample of one or more of the crop parts being analyzed. They give no indication, however, of the number of duplicate analyses that went into the data. They did not outline methodology for collecting the soil or water samples; therefore, we might assume a soil or water aliquot was taken from blending samples at a given location. Again, no mention was made of whether duplicate analyses were performed. Details for analyzing the filter papers for lead values are also lacking. This section of the report should be more inclusive so the reader will have some appreciation for possible variations within the analytical procedures. For easier comparisons with other work the crop values should have been reported as pg. Pb per g. dry wt. The geographic location chosen for the cauliflower and tomato studies was a good one in relation to traffic density. The finding from land use data, however, that heavy lead contamination from lead arsenate insecticide was present detracted from the main objective of studying the effects of levels of airborne lead particulates. The area in which cauliflower and tomato were grown was more intensively studied than the other areas and includes much of the meteorological data. Soil studies at this site suggest that higher lead levels were found at the line 50 feet from the highway. However, high levels were found uniformly from 250 to 1200 feet. The variability was so great that the higher values at the 50 foot line might not be significant even though the average value was about 50% higher than at the other distances. Soil lead levels 26 inches beneath the surface of the soil and
levels indicated in the soil profiles suggest uniform mixing with little or no mobilityof the lead within the soil. Thus,water soluble forms probably are not present. Considerable effort was spent at the above field site trying to correlate concentrations of airborne lead at various distances from high traffic density highways with wind speed and direction. A correlation was found between wind direction and concentrations of airborne lead. Although not dicussed, the tabular results suggest this correlation would be interrelated with wind speed, traffic density at given times, and other weather parameters (such as precipitation). The basic correlation of wind direction and airborne lead particulate concentrations was well shown in Figure 1. A study of another site gave similar curves but much higher lead levels. Data from the second site also showed a greater rate of lead particulate fallout, which could be directly related to wind speed. It would be interesting to know more about the second site-especially information on traffic density. Analyses of cauliflower lead concentrations showed a good correlation with concentrations of both airborne and soil lead. Curves for lead concentrations of whole cauliflower and unwashed tomato are similar to the curves for airborne lead in relation to distance from the highway. These values could be from contamination, but three of the values are well above those of comparable whole cauliflower analyses. The washed tomato fruits have higher lead close to the highway, which could represent absorption of airborne soluble lead into the leaf or fruit tissues or the uptake of small amounts of lead from the soil. The studies on cabbage and strawberries were evidently set up to study crops at some distance from high traffic density highways, because results from the cauliflower and tomato would suggest that at one mile downwind and a half mile upwind the road effects would be lost. The value of these studies is lost because there were no comparable studies with these crops near high traffic density highways. Some interesting data were generated from the cabbage at the intersection of the north and west roads with traffic densities of about 5000 cars per day. The soil lead data suggest that the north road travelers have to stop at the west road, which would be a through road. High levels of soil lead within 200 feet of the intersection suggest a slowdown of traffic along with acceleration as cars move east from the stop sign. This is conjecture, but could explain the results presented. The soil levels close to the intersections are much higher than one would expect from the traffic density listed. The lead levels of the outer cabbage leaves at the site closest to the intersection could be exVolume 4, Number 4, April 1970 331
plained in the same way and are the highest crop level reported in the paper (excluding unwashed orange peel data). Thus; a case might be made for a more thorough study a t major stopgo intersections. The strawberry data showed no correlation between distance from the highway and lead levels of either the fruit or the top layer of soil. With a traffic density of 1000 cars per day, no special effects should have been expected. Irrigation water at the strawberry site was sampled and found to contain no lead. Lead was found after the water ran in furrows for about 200 feet, but no attempt was made to determine if the lead was soluble in the water or merely part of the suspended particulate. It would be interesting to check for soluble lead in the soil. The authors state that although the lead appears to be immobile in the soil, it could be available to the plant. This should be determined for all sample areas by growing test plants in the soils away from contaminated air. The orange study was perhaps the best designed. The lead data for both washed and unwashed orange peel from the two sides of the highway correlated well with wind direction at the time of highest highway density. However, except for the 100foot interval, neither side of the highway showed a correlation of orange peel lead levels with distance from the highway.
The authors state that the results clearly show all positive lead values for the orange meat are a result of contamination when the orange was peeled. This conclusion does not appear warranted from the results presented. It could be suggested that some absorption takes place or that some translocation from root absorption might occur. In summary, the authors have presented good evidence supporting their thesis that particulate lead from automobile exhaust contaminates crops growing in the vicinity of high traffic density roadways. Their contention that this contamination is entirely a surface coating is not well substantiated. Some of the results are inconclusive and others suggest a surface adsorption or the absorption of some lead into the plant parts studied. The possibility of the uptake of lead from soils is not eliminated. Soil lead levels in the vicinity of high traffic density highways could eventually become of concern. Although lead appears to be immobile in the soils, some work suggests that the lead does become available to some crops at certain high concentrations. The levels of lead in crops reported in this study are well below those suggested for human or animal consumption. Possibly the lead from automobile exhaust is not yet of critical concern.
Discussion Relationship of Automotive Lead Particulates to Certain Consumer Crops H. L. Motto College of Agriculture and Environmental Science, Rutgers University-The
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he objective of the investigations reported in this paper was to examine the interaction of airborne lead and consumer crops. The authors correctly conclude that in order to investigate such interactions, studies must be conducted on lead in air, soils, and crops. The studies conducted, however, appear to be lacking in several aspects. The results obtained for the lead content of air, soils, and plants with respect to distance from highways are quite similar to what we have found in New Jersey. The studies in California and New Jersey support each other in this aspect. The levels of lead found in the two studies, however. are quite different. The variations may be due to several reasons. Lead in air in New Jersey may be higher due to more industry, a denser population, or to the fact that in this study the air sampling device was facing downward. The authors give no reasons for their sampling technique and the writer fails to see any reason for using this system. This sampling technique may not have collected the total particulate matter in the air. The lower levels of lead in soil found in this study may also be due to generally lower lead levels, or due to the method used to extract lead from the soil (10% HNO, in contact with the soil for three days). This method will not extract all the lead and may remove variable percentages from different soils. A method that would measure the total soil lead should remove any effects of differences in soil properties regardless of soil or location. The authors chose to analyze only the edible portion of the 332 Environmental Science & Technology
State University of New Jersey, New Brunswick, N.J.
crops studied. Except for cabbage, this was the fruiting bodies of the crops. The inorganic composition of such plant parts is influenced relatively little by the environment and more so by the genetics and physiology of the plant. Analyzing only these plant parts has led the authors to conclude that lead is not absorbed by plants but exists only as a dust coating on the plant surfaces. Analyzing other plant parts such as leaves and roots, which are better indicators of the inorganic composition of the plant’s environment, possibly would have brought them to a different conclusion. Certainly only the edible portion of the plant may be important in regard to human consumption, but, in studies of the interactions of lead and plants, the total plant must be examined. In the reported investigation, the collection of air samples covered only a period of three days. Lead content of air is extremely variable with time (as is shown by the authors’ data). With respect to plants, it is not the short-term lead concentration in air that is important, but rather the average lead concentration over the growing period of the plant. A longer sampling period is necessary to establish the amount of lead in contact with the plant. In summary, Schuck and Locke demonstrate adequately the distribution of lead with respect to highways. However, it is their conclusion that lead is not absorbed by plants that is not warranted by the data shown. Perhaps a more exhaustive study using different techniques would have produced a different conclusion.
