UCLA Radiocarbon Dates X

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Hierarchical sampling of multiple strata: an innovative technique in exposure characterization

Abstract Sampling of multiple strata, or hierarchical sampling of various exposure sources and activity areas, has been tested and is suggested as a method to sample (or to locate) areas with a high prevalence of elevated blood lead in children. Hierarchical sampling was devised to supplement traditional soil lead sampling of a single stratum, either residential or fixed point source, using a multistep strategy. Blood lead (n ¼ 1141) and soil lead (n ¼ 378) data collected under the USEPA/UCI Tijuana Lead Project (1996)(1997)(1998)(1999) were analyzed to evaluate the usefulness of sampling soil lead from background sites, schools and parks, point sources, and residences. Results revealed that industrial emissions have been a contributing factor to soil lead contamination in Tijuana. At the regional level, point source soil lead was associated with mean blood lead levels and concurrent high background, and point source soil lead levels were predictive of a high percentage of subjects with blood lead equal to or greater than 10 mg/dL (pe 10). Significant relationships were observed between mean blood lead level and fixed point source soil lead (r ¼ 0:93; Po0:05; R 2 ¼ 0:72 using a quadratic model) and between residential soil lead and fixed point source soil lead (r ¼ 0:90; Po0:05; R 2 ¼ 0:86 using a cubic model). This study suggests that point sources alone are not sufficient for predicting the relative risk of exposure to lead in the urban environment. These findings will be useful in defining regions for targeted or universal soil lead sampling by site type. Point sources have been observed to be predictive of mean blood lead at the regional level; however, this relationship alone was not sufficient to predict pe 10. It is concluded that when apparently undisturbed sites reveal high soil lead levels in addition to local point sources, dispersion of lead is widespread and will be associated with a high prevalence of elevated blood lead in children. Multiple strata sampling was shown to be useful in differentiating among sources by site-specific association to mean blood lead and the prevalence of elevated blood lead at the regional level.

Natural skeletal levels of lead in Homo sapiens sapiens uncontaminated by technological lead

Lead, Ba and Ca concentrations were determined in tooth enamel, femur and rib from buried skeletons of PreColumbian Southwest American Indians, 10 subjects who lived 1000 years ago on the Pacific coast at 34°N, and 13 subjects who lived 700 years ago in a desert valley tributary of the Colorado River at 37°N 111°W, both groups living in environments uncontaminated by technological Pb. For the coastal tribe, average Pb/Ca ratios were 1.1 × 10^(−7) in enamel, 2.3 × 10^(−7) in femur and 4.7 × 10^(−7) in rib, while Ba/Ca ratios were 1.2 × 10^(−5) in enamel, 32 × 10^(−5) in femur and 38 × 10^(−5) in rib (wt ratios). For the desert tribe, average Pb/Ca ratios were 4 × 10^(−7) in enamel, 11 × 10^(−7) in femur and 37 × 10^(−7) in rib, while Ba/Ca ratios were 1.1 × 10^(−5) in enamel, 7.5 × 10^(−5) in femur and 6.2 × 10^(−5) in rib. It is shown that biologic levels of Pb and Ba in buried femur and rib at both burial sites and in buried enamel at the Arizona site are obscured by excessive diagenetic additions of Pb and Ba from soil moisture. It is shown that one-third of the Pb in enamel at the Malibu site is biologic, yielding a skeletal Pb/Ca (wt) ratio of 4 × 10^(−8). This is equivalent to a mean skeletal concentration of 13 ng Pb g^(−1) bone ash, and a mean natural body burden of 40 μg Pb/70 kg adult Homo sapiens sapiens, uncontaminated by technological Pb. This value is about one-thousandth of the mean body burden of 40 mg industrial Pb/70 kg adult American today, which indicates the probable existence within most Americans of dysfunctions caused by poisoning from chronic, excessive overexposures to industrial Pb

Jasper Procurement, Trade, and Control in Orange County: Comments and Observations

No other issue in Orange County archaeology has been as intense and sustained as that surrounding the question of prehistoric jasper procurement/ trade/control. The once-conventional wisdom that jasper recovered from Orange County sites was obtained in trade from desert regions to the east (McKinney 1967:27) went uncontested (e.g.. Hudson 1969:27) until Cottrell published her view that Orange County entrepreneurs procured the resource directly from the deserts (Cottrell and Del Chario 1984: 59), thereby sparking a debate that included even source provenience as a point of contention (Koerper and Fife 1985). The controversy continues, focusing on the following related hypotheses: (1) jasper found at Tomato Springs, Orange County (Fig. 1), was procured by local entrepreneurs engaged in forays into the Mojave Desert or beyond to acquire unmodified stone weighing as much as 11.67 kg. and (2) the Tomato Springs site (CAOra-244) was the primary or sole center for production and distribution of artifacts of jasper in coastal southern California (Cottrell 1985). Two critiques of Cottrell's jasper procurement/trade scenario (Koerper et al. 1987; Shackley 1987) posed numerous questions regarding lithic procurement, resource control, and tool manufacture. A recent commentary (Cottrell and Wagner 1990) neglected most of the concerns proffered by Koerper et al. (1987) and Shackley (1987) but rather focused on macroscopic and microscopic examination of Tomato Springs material to conclude that the Ora-244 jaspers are allochthonous to the Peninsular Ranges and therefore must have come from either the Mojave or Colorado desert. Here, we discuss those important issues not addressed by Cottrell and Wagner (1990). Next, petrological, petrographical, paleontological, and geochemical observations are offered to support a hypothesis of local jasper procurement. Included are data derived from scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDX) that indicate a high degree of correlation in morphology, crystallinity, and trace element chemistry between a sample of local float jasper and a debitage specimen from Ora-244