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LEAD POISONINGBy F.Ahmadzadeh occupational medicine especialistLead is an ancient metal. Because of its malleability and low melting point, humans have used lead since prehistoric times to make statues, jewelry, water pipes, and drinking vessels.In the mid-1970s, nearly 200,000 tons of lead were consumed annually in gasoline in the United States. Virtually all of this lead was emitted into the environment from vehicles in a finely particulate form and caused widespread contamination of air, dust,soil, drinking water and food crops.OCCUPATIONAL LEAD EXPOSUREIn the United States more than 3 million workers are estimated by NIOSH to be potentially exposed to leadin their work.Occupational exposure to lead is regulated in the United States by the OSHA lead standard, first promulgated in 1978. This standard sets limits on air-borne lead exposure as well as on permissible levels of lead in blood.Major occupations associated with risk of inorganic lead poisoning

A major industrial group that previously had beenexempted from the protection of the United States leadstandard were construction workers. Major outbreaks oflead poisoning were observed among workers who cut leadpainted steel structures such as bridges with oxyacetylene torches and among renovation workers who remove lead paint from older homes.In 1993, the OSHA lead standard was extended to cover the construction and demolition trades.Measurement of occupational exposureAssessment of occupational exposure to inorganic leadrequires measurement of lead levels in both air and blood.The OSHA standard (1993) for the permissible exposure level of lead in workplace air is 50 micrograms/m3,expressed as an 8-hour time-weighted average .This standard can no longer be considered adequately protective of workers health, because lead toxicityhas been observed in workers whose lead exposures donot exceed the current OSHA standard. Fetal lead poisoning can occur in the offspring of female lead workers well below this level . Measurement of the blood lead level complements determination of lead levels in air.

By the OSHA lead standard, anyone found to have a blood lead level of 50 micrograms/dl or above must be removed from the high-exposure job (termed medical removal protection).

A worker is not allowed to return to a high-exposure job until the blood lead level has fallen to below 40 Gr/dl.Air:Air lead standard in the United States is 1.5 gr/m3

ENVIRONMENTAL LEAD EXPOSUREMotor vehicles were the major contributor of lead emissions to the air (TEL).MTBE (Methyl tert-butyl ether)EthanolPaint: Some lead compounds are colorful and are used widely in paints and lead paint is a major route of lead exposure in childrenSoil May be caused by: broken-down lead paint, residues from lead-containing gasoline, used engine oilPesticides used in the pastfrom nearby industries such as foundries or smelters

Water

1.From the atmosphere or soil ( end up in groundwater and surface water.)

2.from plumbing and fixtures (chloramines , which were adopted as a substitute for chlorine disinfectant due to fewer health concerns, increase corrositivity )In the US, 1420% of total lead exposure is attributed to drinking water .

safe drinking water standard for lead is 0.15 mg/l (15 parts per billion).Lead-containing products

Lead can be found in products such as kohl, an ancient cosmetic.from some toys. In 2007, millions of toys made in China were recalled from multiple countries owing to safety hazards including lead paint. Lead is commonly incorporated into herbal remedies such as Indian Ayurvedic. preparations and remedies of Chinese origin.In the general population, children are the group most heavily exposed and most susceptible to the toxic effects of lead.

Who is most Vulnerable to the Effects of Lead? Exposure to lead can cause behavior problems and learning disabilities in young children and can also affect the health of adults.

Imported toys tainted with lead have made news recently. The lead can be both in the paint and in the plastic itself. Sucking or chewing on the toy -- or getting lead on the hands -- can be enough to poison a child.www.recalls.gov The mean blood lead level of children in the UnitedStates is about 3 micrograms/dl.

A decline of 90% in bloodlead levels occurred among American children from 1976 to 1997 as a consequence of removal of lead from gasoline.

According to the Centers for Disease Control and Prevention(CDC), blood lead levels of 10 micrograms/dl and higher in children indicate excessive exposure.Blood leadlevels of 10 g/dl and above are associated with subclinical lead toxicity in children.

Lead-based paint is the major concentrated, high-dosesource of lead for American children. Since 1979, themaximum allowable concentration of lead in domesticpaint has been regulated by the United States ConsumerProduct Agency at 0.06 parts per million.The new dust standard : 40 micrograms/ft2 for floors 250 micrograms/ft2on window sillsBelow 400 ppm in soil of play areas 1200 ppm average for bare soil in the rest of the yard.Hand-held portable blood lead instrumentsportable, hand-held x-ray fluorescence (XRF) detectors.

CLINICAL EFFECTS IN ADULTSAcute inorganic lead toxicityIntense occupational exposure to lead over a brief period of time . abdominal colic, constipation,fatigue, hemolytic anemia, peripheral neuropathy,alteration of central nervous system function Signs and symptoms

gingival lead line acute encephalopathy with coma, convulsions, and papilledema may occur;

In milder cases :

only fatigue, headache or personality changes may be evident as manifestations of the neurologic toxicity of lead.Mild liver involvement, limited to modest elevations in serum glutamic-oxaloacetic transaminase (SGOT).musculoskeletal pains and arthritic.Basophilic stippling in the red blood cells.(occur in blood lead level 70 micrograms/dl or more)

Chronic inorganic lead toxicityArthralgias MyalgiasHeadacheWeakness Depression loss of libido, impotence, Vague gastrointestinal difficulties. Thyroid and adrenal function often are depressed. Hypertension Sperm counts can be depressed in men and fertility reduced in women.

Signs and symptomsRenal function may reveal impairment of glomerular clearance; decreased tubular urate clearance resulting in hyperuricemia is common. Late effects of inorganic lead intoxication include : chronic renal failure, gout, chronic encephalopathy, and hypertension.Subclinical toxicity( low-dose exposure )May cause harmful effects to health in the absence ofsymptoms and signs that are evident on the standard Clinical examination.1.Hematologic toxicityAnemia :presence of anemia is not required for a diagnosis of lead poisoningThe severity and prevalence of lead-induced anemia are correlated directly with the blood lead level in both adults and children.The effects of lead on organ system FunctionLead-induced anemia is the result of multiple mechanisms:

impairment of heme biosynthesis : 1.Inhibition of the cytoplasmic enzyme, d-aminolevulinic acid dehydratase (ALA-D). 2.The mitochondrial enzyme ferrochelatase. That results accumulation of zinc protoporphyrin [ZPP]) in the erythrocytes.

Acceleration of red blood cell destruction.

inhibition of erythopoietin production in the kidney.2.Neurologic toxicity(Neurologic toxicity of lead in adults)

Peripheral motor neurologic toxicity:

1. Extensor muscle palsy with wrist drop or ankle drop 2. Asymmetry

Unlike other toxic neuropathies, this motorneuropathy may show leftright asymmetry.

Mild to moderate sensory dysfunction also may be evident in lead neuropathy, and in such cases the clinical picture is one of mixed motorsensory neuropathy, often with asymmetric features.In the central nervous system( high-dose acute exposure to lead ) causes encephalopathy characterized clinically by obtundation coma, and convulsions Among persons who recover from acute lead encephalopathy, a high proportion are left with significant neuropsychologic deficits, including reduced intelligence, shortened attention span, and instability of mood.Impairment in central neurologic function in adults at doses insufficient to produce clinical encephalopathy:

-Fatigue

-Short-term memory loss

-Depressed mood3.Renal toxicityAcute Fanconi syndrom

Vit .D defficiency At blood lead levels below 25 gm/dl, lead inhibits the metabolic activation (hydroxylation) of vit. D

At blood lead levels of 4080 gm/dl, lead induces the formation of dense intranuclear inclusion bodies consisting of a lead protein complex in cells lining the proximal tubules.Hyperuremic gout resulting from increased reabsorption of uric acid by the tubular cells.

Chronic nephropathy, which may progress to kidney failure.

Chronic low-level lead exposure: abnormal urinary excretion of n-acetyl glucosaminidase (NAG) 4. hypertension

long-term, high-dose exposure to lead associated with an increased incidence of hypertension and cerebrovascular disease5.Reproductive toxicity of lead

Decreased sperm counts, abnormal sperm morphology, and decreased sperm motility when lead levels were above 40 micrograms/dl.

increased incidence in spontaneous abortion among female lead workers as well as in the wives of male lead workers.

lead may cause neurologic damage to the fetus at blood levels as low as 510 micrograms/dl, substantially below the current OSHA standard for blood levels of lead in Workers. The prevention of fetal lead encephalopathy requires that blood lead levels of prospective mothers be kept below 10 micrograms/dl, not only during pregnancy but also in the years preceding conception.

If a woman who has previously had elevated blood lead levels wishes to become pregnant, it may be reasonable to recommend either an x-ray Fluorescence examination of bone to determine body burden of lead .6.Carcinogenicity

group 2A probable human carcinigenRenal cancerBrain tumor Organic lead

TEL use as antiknock in gasolineTEL produce a syndrom difrenet from inorganic lead poisoningCause : insomnia, anorhexia, muscle irritability,aggitated encephalopathy,tremor and ataxia

Clinical evaluation

Clinical evaluation strategy for adult

The diagnosis of in organic lead intoxication in adults requires:

1- demonstration of excess lead absorption 2-documentation of impairment in an organ system consistent with the effect of lead 3-exclution of other cause of impairment Lead is not distributed homogeneously in the human body It is dispersed amonge several physiologically distinct compartment.

Blood lead Lead Distribution in human body1% of body burden half life 36 daysSingle best indicator of recent lead absorptionNormal adult lead level is below 10gr/dlClinical symptom appear at 30-40 gr /dlAt 50 gr /dl worker must immediately remoev from exposure and they can not return to work their level have fallen below 40 g/dlLead in calcified tissue of skeleton and teeth:90-99% of absorpted lead ( 70% in children) .Half life 15-20 years.blood lead level appears principally to reflect release of stored from deep tissue compartment to blood .K-shell x-ray fluorescence (XRF) analysis is a accurate, non-invasive and relatively rapid assessment of chronic lead exposure.

Zinc protoporphyrin (ZPP) or free erythrocyte protoporphyrin (FEP) levels reflect the toxic effect of lead on the erythrocytic enzyme ferrochelatase.

A combination of normal FEP value and high blood lead level indicates very recent exposure that has not yet had opportunity to poison heme metabolism.

Because the ZPP level remains elevated long after the blood lead level has fallen, this test does not discriminate between recent and past exposure.Zinc protoporphyrinthe diagnosis of lead poisoning cannot await the appearance of anemiaAnemia:Basophilic stippling in the red blood cells is seen in mostpatients with acute hemolysis and occasionally in patientswith chronic hemolytic syndromes; it is not specific tolead poisoning.Basophilic stippling: Lead lines on the gums are uncommon except in cases of severe poisoning and may be difficult to recognize in patients with poor dental hygiene.Lead lines: Complete blood counts and routine blood chemistry should be performed as baseline in asymptomatic workers.Other baseline tests include creatinine clearance,BUN, and uric acid.Blood pressure should be measured regularly.Blood lead levels should be obtained on a periodically. If the whole blood lead levelexceeds 40 micrograms/dl, tests should be repeatedmonthly; blood lead levels over 50 micrograms/dl require immediate removal of workers from lead-exposure, andthey may not return to work in a lead-exposed job untilthere have been two lead-levels below 40 micrograms/dl Measurement of the urine lead level is of little value inmonitoring populations exposed to inorganic lead; the testis too highly variable to be reliable.

Hair leadhair lead analysis is not considered reliable for monitoring purposes.urine lead Clinical evaluation strategy: organic lead

Organic lead (TEL) intoxication is difficult to diagnose without a history of exposure.Blood or urine lead levels and FEP levels are not predictably elevated in TEL poisoning.MANAGEMENTManagement of acute lead poisoning in adults:Immediate removal from exposure to lead.

chelation (intravenous calcium EDTA and Oral chelation with DMSA ).

Chelation should be considered for blood levels greater than 80 micrograms/dl, especially when there are central or peripheral nervous system effects.

For blood lead levels of 6080 micrograms/dl, decisions regarding chelation should be made on a case-by-case basis.Management of chronic lead IntoxicationStudies are needed to confirm whether chelation therapy of adults with chronic lead intoxication results in amelioration of long-term effects such as gout, hypertension or renal insufficiency,The administration of chelating agents to persons with chronic lead intoxication must be approached with great care, because they often have impairment of renal function.Chronic administration of oral chelation agents to workers who continue to be exposed to unacceptably high levels of lead in their work has been used by some unscrupulous employers as a means of reducing blood lead levels while not reducing levels of lead in air in the workplace.Management of organic lead poisoning

The treatment for TEL poisoning is primarily support;chelation with calcium EDTA has been tried with variableefficacy. Sedation and careful observation are required insevere cases, often for prolonged periods.Prevention of occupational lead PoisoningAir-born exposure to both organic and inorganic lead inthe workplace must be strictly limited by enclosure ofhazardous processes, ventilation, and other engineeringcontrols.OSHA lead standard mandates that occupational exposures to lead be held below 50 gr/m3 of air, expressed as an 8-hour,TWA.

However, studies have shownclearly that toxic adverse effectscan occur in lead workers at levels of exposure below this standard.clinical or subclinical toxic effects can occur at and below the current biologic exposure limitof 50 micrograms/dl of whole blood. A physician may remove a worker with a lower blood level if lead Poisoning is diagnosed and restrict the worker from return to Exposure until approved by the physician.

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