Exposure to lead, which generally occurs from lead-based paint chips from
older buildings, mining, smelters, and municipal waste incineration, can occur
from inhalation of polluted air and dust and from the ingestion of lead in food
and/or water. The United States banned lead-based paint in 1977 in residential
properties and public buildings along with toys and furniture that contained lead
paint.
Symptoms of lead poisoning include failure of the blood to make
hemoglobin, which results in anemia (low red blood cell count), endocrine
(hormone) disrupters, mental retardation and disabilities, hypertension (high
blood pressure), miscarriages and/or premature births, and even death at
relatively low concentrations.
NITROGEN OXIDES (NOx)
NOx is a generic term for NO (nitric oxide) and NO 2 (nitrogen dioxide), which
are produced from the reaction of nitrogen and oxygen gases in the air. NOx
gases are formed whenever nitrogen occurs in the presence of high temperature
combustion (e.g., forest fires, internal-combustion engines, lightning, power
station boilers, and volcanoes). NOx gases react to form acid rain; they are also
central to the formation of tropospheric ozone.
When NOx and volatile organic compounds (VOCs) react in the presence of
sunlight, they form photochemical smog, a significant form of air pollution,
especially in the summer. Agricultural fertilization and the use of nitrogen-fixing
plants also contribute to atmospheric NOx by promoting nitrogen fixation by
microorganisms.
NOx should not be confused with nitrous oxide (N 2 O), which is a greenhouse
gas. Nitrous oxide is a major greenhouse gas and air pollutant, with levels of
N 2 O having increased by more than 15% since 1750. Considered over a 100-
year period, N 2 O is calculated to have about 300 times more impact per unit
mass (global-warming potential) than carbon dioxide.
Agricultural croplands contribute about 70% of the total nitrous oxide (N 2 O)
emissions. Nitrous oxide (N 2 O) is produced naturally:
■ In the soil during the process of nitrification (the oxidation of ammonia
[NH 3 ] to nitrite [NO 2 – ] and nitrate [NO 3 – ]).■ By denitrification—the process whereby ammonia (NH 3 ) is oxidized to
nitrite (NO 2 – ) by bacteria of the genus Nitrosomonas.