|
1
<br /> composition . The egUlllbrlUm solubility of Iead with carbonate .
<br /> sulfate , and sulfide is low . Over most of the normal pH range ,
<br /> 16 lead carbonate and lead sulfate conct;rol solubility of lead in
<br /> ' aerobci conditons , and lead sulfide and the metal control
<br /> solubility in anaerobic conditions . Lead is strongly complexed to
<br /> organic materials present in aquatic systems and soil . Lead i.n
<br /> soil is riot easily taken up by plants, and therefore its
<br /> availability to tresetrial orgnaisms is somewhat limited .
<br /> Bioaccumulation of lead has been demostrated for a variety of
<br /> organisms, and bioconcentration factors are within the arange of
<br /> 100-1 , 000 . Microcosm studies indicate that lead is not
<br /> biomagnified through the food chain. Biomethylation of lead by
<br /> microorganisms can remobilize lead to the environment .
<br /> In conclusion, the mechanisms of lead transport through the
<br /> Environment is complex and not predictable without abundant
<br /> chemical , biological , and physical data describing the specific
<br /> environment.
<br /> ' HEALTH IMPLICATIONS OF LEAD IN THE GROUNDWATER
<br /> The last sampling round indicated that the lead concentrations in
<br /> the groundwater is attentuating due to unknown biological ,
<br /> physical , or chemical degradation or adsorption mechanisms .
<br /> However , since the maximum contaminant level goal ( MCLG) under the
<br /> Safe Drinking Water Act is 0 .0 mg/l , any detection of lead in the
<br /> groundwater should be reflect a human health concern .
<br /> The health effects of lead exposure often occur at blood lead
<br /> ' levels so low as to be essentially without a threshold . The EPA
<br /> thus considers it inappropriate to develop a RfD ( reference dose )
<br /> or RfC ( reference concentration ) for the noncaroinogenic effects of
<br /> inorganic lead ( IRIS, 1993) _ Chronic lead poisoning can be divided
<br /> into 6 categories : gastrointestinal or abdominal , neuromuscular ,
<br /> CNS (central nervous system ) , hematological , renal and other . They
<br /> ' may occur separately or in combination .
<br /> Symptoms of overexposure may include lassitude, insomnia , paleness ,
<br /> lack of appetite , pica , low weight , malnutrition , constipation ,
<br /> ' abdominal pain , colic , vomiting , tremors , paralysis of the wrists ,
<br /> and permanent brain damage. Chronic exposures resulting in blood
<br /> lead levels of 40-60 9/dl have been accompanied by symptoms of
<br /> slowed reaction time, decreased fertility , abnormal menstrual
<br /> cycles , impotence , decreased sex drive , sterility , fatigue ,
<br /> headache , irritability , anxiety , hearing difficulty , and loss of
<br /> sort term memory. Studies have linked low level lead exposure , as
<br /> ' low as 15 g/dl blood, with intelligence reduction in children .
<br /> Lead is a potential mutagen and teratogen , and a probable
<br /> carcinogen ( EPA Class B2 ) as evidenced from animal studies (ATSDR ,
<br /> 1991 ) .
<br /> In 1988, 3 to 4 million Afflerican children continued to be exposed
<br /> ' to levels of lead in the environment that put them at risk of
<br /> adverse health consequences . In 1985 , the EPA said that 42 million
<br /> Americans drink water with higher lead content than recommended .
<br /> EPA' s Rural Water Survey found lead to exceed drinking water
<br />
|