LEADLEAD

Francine Lortie-Monette, MD, MSc, CSPQ, MBA

Department of Epidemiology and Biostatistics

University of Western Ontario

2003

LEAD (heme synthesis inhibitor)LEAD (heme synthesis inhibitor)

Concentrations increased substantially during the Industrial Era.

But decreased with the removal of lead from gasoline, paint (interior paint: 50’s, exterior paint: 70’s) and soldered food cans.

Routes of Occupational ExposureRoutes of Occupational Exposure

Inhalation (e.g. due to abrasive blasting, sanding, removal with heat guns, grinding):

nearly 100% of inhaled lead enters the blood

Ingestion (e.g. hand-mouth contact and eating-on-site in construction, battery and refinery workers):

more variable absorption

Lead-using industries / Lead-using industries / occupationsoccupations

Lead smelters and refineries

Glassworks (crystal glass)

Artisan trades (ceramics, although lead-containing glazes are becoming rare)

Lead-using industries / Lead-using industries / occupations (Cont’d)occupations (Cont’d)

Printing, publishing, photocopiers and related industries

Battery making and recycling

Wireworks producing sheathing for wires and cables (although cables now mostly coated with plastic or metal sheathing)

Lead-using industries / Lead-using industries / occupations (Cont’d)occupations (Cont’d)

Pest control (many insecticides formerly contained lead arsenate)

Plastic industries (lead stabilizers)

Radiation shielding (used in X-ray rooms and nuclear reactors)

Building demolition and construction industries – especially where lead-paint is still used for non-corrosive metal coatings (e.g. on ships and bridges) The use of oxy-acetylene cutters for demolition on such structures can create hazardous lead fumes.

Around the House and GardenAround the House and Garden

Houses built before 1950 are most likely to contain large amounts of lead in paint, plumbing pipes and fixtures, in soil around the base of the house, or near old porches and railings.

Home renovations with removal of old paint are a very important cause of lead exposure.

Houses built between 1950 and 1980 may have moderate amounts of lead in paint and plumbing, and in outdoor areas.

Around the House and Garden Around the House and Garden (Cont’d)(Cont’d)

Still:

In 1997: 4.4% of children had elevated blood levels in the USA

Around the House and Garden Around the House and Garden (Cont’d)(Cont’d)

In Ontario: the mean level in children decreased from

0.91 μmol/L (1972) to 0.29 μmol/L (1988)

BUT: 4-8% of Canadian children have elevated blood levels

50% of children had elevated levels in a B.C. site near a lead / zinc smelter

ToxicityToxicity

Lead absorption is not always associated with lead poisoning:

Toxicity varies with:

• Solubility and particle size of the compound

• Conditions of use

Toxicity Examples:Toxicity Examples:

Lead arsenate:

Lead carbonate, monoxide and sulphate:

Lead chromate:

- very toxic

- more toxic than other lead compounds

- Less toxic (low solubility)

Distribution of Absorbed LEADDistribution of Absorbed LEAD

Lead absorbed from the lung or from GI tract is distributed in 3 main compartments:

i. Blood (blood lead levels reflects recent exposure (prior month))

ii. Soft tissues (kidney, bone marrow, liver, brain)

iii. Bone/Teeth (the skeleton = the accumulating reservoir; X-ray fluorescence measurement of lead concentrations is an index of cumulative exposure)

Signs of LEAD AbsorptionSigns of LEAD Absorption

Increased urinary excretion of lead Possibly increased lead blood levels Decreased hemoglobin levels

Health EffectsHealth Effects

Acute / Severe Chronic

Health Effects: Health Effects: Acute / SevereAcute / Severe

anaemia abdominal colic peripheral neuropathy (extensor weakness)

“wrist/ankle drop” central neuropathy with toxic

encephalopathy sterility

Health Effects: Health Effects: ChronicChronic

Blood Forming Organs: anemia

increases the rate of erythrocyte destruction / interferes with heme synthesis

pallor

Health Effects: Health Effects: Chronic (Cont’d)Chronic (Cont’d)

Peripheral nervous system (“paralysis”): decreased coordination slowing of nerve conduction

Central nervous system (prefrontal cortex, hippocampus, cerebellum): decreased auditory sensitivity & visual motor

performance behavioral changes (e.g. attention deficit & memory

problems) sometimes (rare) encephalopathy

Health Effects: Health Effects: Chronic (Cont’d)Chronic (Cont’d)

Kidney / Reproductive:

irreversible nephritis (glycosuria, proteinuria, chronic renal failure and

hypertension risk of fetal damage and of miscarriage

Acute PoisoningAcute Poisoning

Treatment decision based on:– current blood lead level– evidence of current adverse clinical effects– duration of excessive exposure and of symptoms

Chelation if blood lead level rises to 80 g / dL, specially if associated with symptoms / signs of central or of peripheral nervous system dysfunction.

Chelation rarely considered if blood level is below 60 g / dL.

TreatmentTreatment

In general, blood lead levels decrease by about 305 g / dL per week.

Half-life in

blood: (about) 25 days

soft tissues: 40 days

skeletal compartment: (over) 25 yrs

Physical Examination in Physical Examination in Lead-Exposed WorkersLead-Exposed Workers

Blood pressure Pallor Appearance of chronic illness Lead (blue-black) lines on gums Abdominal tenderness Motor/sensory/cerebellar neurological deficits Tremor Cognitive function Mood and affect

Physical Examination in Physical Examination in Lead-Exposed Workers (Cont’d)Lead-Exposed Workers (Cont’d)

For individuals with fertility / reproductive concerns (to exclude other causes of impaired reproductive function):

Degree of sexual maturation Testicular atrophy or enlargement Cryptorchidism Orchitis

PreventionPrevention

Enclosure of the source; ventilation

Respirators

Personal hygiene/laundering of work clothes

Physical Examination in Physical Examination in Lead-Exposed Workers (Cont’d)Lead-Exposed Workers (Cont’d)

Ask also about: Home:

living near plant? lead paint (old house)?

In 2000, the Canada Mortgage & Housing Corp. estimated that 15% of houses built before 1950.

pre-1989 plumbing?

Hobbies:stained glass, furniture refinishing?

Sampling for Lead (residential) Sampling for Lead (residential)

Home entry areasLaundry areasSinks/bathroomsVacuum systemsCarpets/floorsAutomobile carpets

Case ScenarioCase Scenario

Patient who feels tired/lacks energy

Blood work: anemia

Elevated lead blood level

Perhaps subtle signs of peripheral neuropathy

Lowest-effect levels for key lead-Lowest-effect levels for key lead-induced health effects in adultsinduced health effects in adults

Lowest-observed effect level (PbB)2

(g/dL)

Heme synthesis and hematological effects

Neurological effects Effects on the kidney

Reproductive function effects

Cardiovascular effects

100-120Encephalopathic signs and symptoms

Chronic nephropathy

80 Frank anemia

60 Female reproductive effects

Altered testicular function

50Reduced hemoglobin production

Overt subencephalopathic neurological symptoms

Peripheral nerve dysfunction (slowed nerve conduction)

40Increased urinary ALA and elevated coproporphyrins

30 Elevated blood pressure

(White males, aged 40-59)

?

25-30Erythrocyte protoporphyrin (EP) elevation in males

15-20Erythrocyte protoporphyrin (EP) elevation in females ALA-D inhibition

< 10

Lead LevelsLead Levels

Traditional Unit of Measurement in blood: g/dL

International System of Units (SI): mol/L (traditional unit X 0.04826)

Blood Lead Levels (mol/L) Onset of Effect

< 0.5 Usual background level

0.5-2.0 . Neurological development effects in infants & children

. Inhibition of porphyrin enzymes

2.0 Allowable occupational exposure

> 2.0 Altered RBC count

2.0-2.5 Subclinical peripheral neuropathy

3.5-4.0 Clinical peripheral neuropathy

4.0 Encephalopathy (chronic exposure)

7.0 Encephalopathy (acute exposure)

4.0 Early GI symptoms

6.0 Colic