P.1 1974 (including covering contaminated soil with ofthe lead associated with oat tops was directly at­ clean soil and reducing smelter emissions) and tributable to automobile (aerosol) emissions, but it brought about a decrease in blood lead levels that did not distinguish between lead in the edible por­ were measured a year later. The details ofthe blood tion (grain) and lead on the hulls or chaff.27 This lead levels and their significance are presented in same study reported that lettuce grown in the Salinas Chapter 12. The conclusion to be drawn from this Valley had 3 to 25 ppm lead (dry weight) associated study (and from the similar studies referred to with it, whereas the soil lead content was only 10 above) is that people who live in the vicinity ofa ma­ ppm. The lead content in the lettuce was reported to jor industrial source of lead (e.g., a smelter) are ex­ be 0.15 to 1.5 ppm on a fresh weight basis. The posed to abnormally high lead concentrations. limited data accumulated were used to deduce that the excess lead was delivered to the lettuce by aerial 7.4 DIETARY EXPOSURES emission from autos, and that removal of lead from 7.4.1 Food automobile exhaust would reduce the lead content 27 The route by which most people receive the of the lettuce by as much as 80 percent. In other largest portion of their daily lead intake is through areas, the contribution would be smaller. Though foods, with estimates ofthe daily dietary lead intake these figures may be accurate, they are based on for adult males ranging from 100 to 500 /Ag/day.26 some rather tenuous assumptions that are not well Only a fraction of this ingested lead is absorbed, as supported by observation and very limited data. The discussed in Chapter 10. estimates must thus be considered with caution. The sources of the lead content of unprocessed Moreover, one cannot extrapolate from lettuce or vegetable foods have been noted earlier (Section oats to all crops. 6.4.3). Studies of the lead associated with crops The possible connection between air lead and (near highways) have shown that both lead taken up food lead may be underscored by comparisons be­ from soil and aerosol lead delivered by deposition tween leafy vegetables and food grains. Studies have are found with the edible portions of common shown that the edible portions of grains absorb very vegetable crops. However, there is enormous little air lead,32 whereas the leafy vegetables retain variability in the amount of lead associated with appreciable quantities.2729 An FDA survey34 shows such crops and in the relative amounts of lead in and that grains contain approximately 20 percent as on the plants. Several factors are involved, the most much lead as the leafy vegetables. It cannot be con­ prominent of which are: the plant species, the traffic cluded, however, that 80 percent of the lead in all density, the meteorological conditions, and the local leafy vegetables derives directly from air because soil conditions.2733 The variability induced by the difference must also reflect species-dependent differences in the above factors, coupled with the differences in uptake from soil. fact that many studies have neglected differentiation An overall analysis ofthe data available supports between lead on plants versus lead in the plants, the contention that plants grown near busy highways makes it difficult to generalize. Data of Schuck and consistently have more lead in and on them than 29 Locke suggest that in some cases (e.g., tomatoes those in other areas. This difference is typically very and oranges), much of the surface lead is readily hard to detect at distances greater than about 100 to removed by washing. But as noted in Section 6.4.3, 200 m from the highway, thereby reflecting the fact this is not universally true; in some cases much more that large percentages of the aerosol lead fall out vigorous washing procedures are required. near roadways. It appears reasonable to point out In view of the wide variability of soil conditions that the vast majority of edible crops marketed in (pH, organic matter, cation exchange capacity, this country are grown at distances of more than 100 phosphorus content, etc.), of meteorology to 200 m from the highway and that much of the (especially wind conditions and rainfall), and ofthe aerosol lead can be removed from association with effects of species diversity on the routes of lead ac­ the plants by processing. Clearly there are excep­ cumulation, only crude general correlations between tions that will influence both sides of the question. air lead levels and food crop lead levels are possible. For the present, however, the available data are not This is influenced by the fact that the lead associated sufficient to permit the quantitative estimate of the with plants may be derived from natural sources, contribution of automotive lead to foodstuffs on a from automotive sources, and from other sources national or even regional scale. such as manufacturing or combustion. One study in The concentrations of lead in various food items Southern California reported that 60 to 70 percent are highly variable, and as much variation is found 7-9 P.2 within specific food items as between different food Canned pet foods have been found to contain 0.9 categories. Schroeder and Balassa,35 in a study of to 7.0 ppm lead (approximately 900 to 7,000 American foods, have found that the ranges are 0 to /xg/liter),40 and 18 products averaged 2.7 ppm (ap­ 1.5 mg/kg (ppm) for condiments, 0.2 to 2.5 mg/kg proximately 2700 /xg/liter). Apart from the possible for fish and other seafood, 0 to 3.7 mg/kg for meats toxic effects on pets, the products pose a hazard to and eggs, 0 to 1.39 mg/kg for grains, and 0 to 1.3 persons who may include them in their own diet. mg/kg for vegetables. All of these values refer to The lead content in milk is of special interest unprocessed foods. A British report36 on lead in because it is a major component of the diets of in­ foods describes similar ranges for meat and eggs, fants and young children. The FDA survey37 found grain products (flour and bread), and vegetables; lead concentrations in whole milk ranging from 10 but concentrations up to 14 mg/kg were found in to 70 tig/liter and averaging about 20 pig/liter. In a condiments, and up to 18 mg/kg in certain shellfish. recent study by Ziegler et al.,41 seven samples of The amount of lead taken in with food varies from baby formula and three samples of whole cow's milk person to person. It depends on (a) the total amount were analyzed in duplicate. Mean concentrations of of food eaten, (b) the history of the food during lead were 18 /xg/kg (range 15 to 20) in formula and growth, (c) its opportunity to acquire intrinsic lead 10 /xg/kg (range 7 to 15) in milk (1 /xg/kg is approx­ (absorbed from soil or water) and extrinsic lead imately 1 /xg/liter). Lead concentration in infant (deposited insecticides or contaminated dusts), and fruit juices ranged from 23 to 327 /xg/kg; in five (d) dietary habits (such as using fresh rather than varieties of strained fruits, it ranged from 13 to 131 canned foods). On a per-weight basis, the dietary in­ /xg/kg; and in seven varieties of strained vegetables, take oflead by children has been shown to be two or lead concentration was 14 to 73 /xg/kg. Tolan and 38 three times that of adults. This additional dietary in­ Elton reported 30 /xg Pb/liter in fresh milk in take is especially significant when the lead added to Great Britain and 50 /xg Pb/liter in canned (evapor­ 39 food by processing and to water by plumbing (vide ated) milk. Michell and Aldous reported a com­ infra) is considered. A 1974 FDA survey of heavy parable average for fresh whole milk purchased in metals in foods37 found relatively high lead con­ New York State —40 /xg Pb/liter. But their results centrations in metal-canned foods. In the adult food for evaporated milk averaged 202 /xg Pb/liter and category, canned foods averaged 0.376 ppm lead, ranged as high as 820 /xg Pb/liter. and non-canned foods averaged 0.156 ppm lead. In Hankin et al.42 suggest an additional food-related the baby food category, canned foods (juices) source of potential lead exposure, again predomi­ averaged 0.329 ppm lead, and foods in jars averaged nantly affecting children. The colored portions of 0.090 ppm. The report of the survey concludes that wrappers from bakery confections, candies, gums, from the age of about 1 year on, canned foods com­ and frozen confections have lead concentrations prise 11 to 12 percent of a person's diet, but they ranging from 8 to 10,100 ppm. The higher con­ contribute about 30 percent of the average dietary centrations are attributed to lead-containing inks. lead intake. In a comparison made in the United 38 No related illnesses were identified, nor was con­ Kingdom, lead concentrations in canned foods tamination of the food implied; but the eating of were found to vary widely with the precise nature of foods from such wrappers and the licking or chewing the food, but they averaged about ten times greater ofthe wrappers were postulated as one more avenue than those in fresh foods.