Anthropogenic lead sources

From Lead in Gasoline. The use of gasoline containing lead as an antiknock agent has been considered the major anthropogenic lead source in Mexico, particularly in large cities and industrial areas. It is estimated that almost 30% of the total lead emitted in Mexico enters the air in and around Mexico City (see section, Fuel additives ), where more than 20% of the population of the country live (20 of an estimated 86 million for 1988). 

The primary source of lead in the environment has historically been anthropogenic emissions to the atmosphere. In 1984, combustion of leaded gasoline was responsible for approximately 90% of all anthropogenic lead emissions. EPA phased out the use of lead alkyls in gasoline, however, and by 1990, auto emissions accounted for only 33% of the annual lead emissions (EPA 1996h). Use of lead additives in motor fuels was totally banned after December 31, 1995 (EPA 1996f). The ban went into effect on February 2, 1996. Atmospheric deposition is the largest source of lead found in soils. Lead is transferred... 

The major organolead compounds found in the environment are the tetraalkyllead compounds and their di- and trialkyl decomposition products. Elevated levels of tetraalkyl-leads have two possible sources either (i) anthropogenic leaded petroleum inputs or (ii) environmental methylation of natural lead compounds. While the former is well established, the latter is the subject of some controversy in the literature. Interest in the environmental methylation process derives from the increased toxicity of methyllead compounds compared to their inorganic analogs. 

Motor vehicle traffic is the main source of anthropogenic lead (Pb) emissions. In humans, toxication causes damage to the nervous system and the kidneys along with other harmful effects (Merian 1991). Lead is preferably absorbed by grass and rape seed. Its content reaches values of more than 5 mg kg-1, while the average lead content of the other plant species is relevantly lower and in some cases below the detection limit. 

Erel, Y., Veron, A., and Halicz, L. (1997). Tracing the transport of anthropogenic lead in the atmosphere and in near-surface tills using isotopic ratios. Geochim. Cosmochim. Acta 61, 4495—4505. Foley, N. K., and Ayuso, R. A. (2008). Mineral sources and pathways of arsenic release in a contaminated coastal watershed. Geochem. Explor. Environ. Anal. 8, 59—75. 

Figure 8 Vertical profiles of dissolved lead in the central North Atlantic (34° 15 N, 66° 17 W data from Schaule and Patterson, 1983), the central North Pacific (32°41 N, 145°W data from Schaule and Patterson, 1981), and the central South Pacific (20°S, 160°W source Regal and Patterson, 1983). Estimates of the atmospheric input at the time of sampling and in ancient times prior to the large anthropogenic lead input are also shown (Flegal and...

Table 33. The most important anthropogenic emission sources of lead to the atmosphere on the global level in 1983 (After Nriagu and Pacina, 1988).

Other information on the sources and dispersion of anthropogenic lead can be derived from the stable isotope ratios of lead (e.g. ° "Pb/ ° Pb) which vary from one mining source to another because of differing Pb/U and Pb/Th for geological sources of lead. In particular, US leaded gasoline for many years had a ° "Pb/ ° Pb ratio of > 1.20, whereas European... 

However, not all of the lead currently in the environment is in a natural state. Lead s usefulness and natural abundance have led to its current position as a ubiquitous pollutant Some 300 million tons of Pb from anthropogenic sources is currently dispersed worldwide (Fig. 4 and Table XIV) (5, 10, 18, 23, 357, 358). Here, we discuss the properties of some of the major minerals of lead and then mrn to a discussion of anthropogenic lead in soil, water, and air. For a more in-depth discussion, the reader is directed to several books that discuss the environmental biogeochemistry of lead in greater detail (3, 47, 359, 360). 

The natural lead in humans is even more difficult to determine. Although the atomic Sr/Ca and Ba/Ca ratios observed in Americans are nearly identical to those of carnivores in the remote ecosystem, the observed Pb/Ca ratio of humans is two orders of magnitude greater than that of the carnivores (Figure 1). Since these carnivores are contaminated at least 50-fold, it would seem that the appropriate correction for humans is 5000. Data from another source (9) show that ancient Peruvians, exposed to very little anthropogenic lead 1600 years ago, have a skeletal Pb/Ca of 3 x 10, compared to that of the average American today, 2100-3500 x 10 . This Peruvian bone value sets an upper limit to the prehistoric human Pb/Ca ratio, since a small but undetermined amount of anthropogenic lead was present. 

Veron A, Church TM, Patterson CC, Flegal AR (1994). Use of stable lead isotopes to characterize the sources of anthropogenic lead in North Atlantic surface waters. Geochim Cosmochim Acta 58 3199-3206. 

The work of the Harrison group on alkylleads in air is perhaps the most persuasive of the reports as to the advocation of an environmental methylating process. Some of the sites whose atmospheric lead was sampled were very remote, such as Harris Island, Outer Hebrides, UK. Air reaching this site should not have any anthropogenic content but concentrations of alkylleads were found to be in the 3-7 ngm-3 range61. There was a higher than normal ratio of alkyl to total lead present here also (from 10-30%). A maritime source of volatile alkyllead was proposed61,62. 

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