Transcript Kielczewski Caroline Bad to the Bone Lead Deposits in Our Skeletons

Bad to the Bone
Lead Deposits in Our Skeleton
Caroline Kielczewski
Lead has a very short half-life; therefore blood lead levels can only be used to diagnose recent
lead exposure. Lead’s half life is 21-30 days; therefore blood only shows recent exposure to lead
(5). BMD, or bone mineral density, refers to the ability of bone to store any mineral including
lead (6). Lead is then stored in the bones. If someone was to move from one isotopic area to
another, their body would not reflect the new lead that they were not absorbing, they would
still have some of the old lead in their system. This is because lead from their previous
environment was stored in their bones, and slowly released back into their system (4). Lead is
accumulated and can be stored for long periods of time in the bones of an individual.
Bones frequently turnover, meaning that the calcium that was stored there during life will be
taken out of the bones and reenter the body once more and be used where it is needed. The
same goes for the lead that is stored in bones. Because lead takes up some of the area that the
calcium should be, it would further weaken the bones. Calcium metabolism rates are not
enough to measure the expected turnover rate of lead in bones. It has also been documented
that blood lead levels will increase when it is expected that calcium metabolism is increasing.
Examples of these times are osteoporosis, lactation, and aging (4). Children and teenagers are
especially susceptible because they have higher metabolic and gas exchange rates, an idea
which proposes that they would come into contact with higher doses more rapidly than adults
(5).
On average lead will stay in someone’s bones from 5-19 years. Of this stored lead only about 2%
will be present in the blood at a time. The rest, around 95% will remain in the bones (3). A
person’s actual turnover rate is related to his or her osteon formation rate, which is dependent
on age. On average this turnover rate is about 2% for most long bones, but around 8% for the
shorter bones. Hard bone, found in long bones, gives the amount of lead that you have been
exposed to during your entire life. Soft bone, found in smaller bones, will give the best measure
for lead that is getting to be released back into the bloodstream (2).
A method to measure long term exposure to lead is to use X-ray fluorescence. Biomonitoring allows for an
estimate of the total amount of lead taken up by the body. To improve upon this technology, a method should be
developed that can discriminate from lead that was deposited into the bones early on in life and later on, without
relying on isotopic ratios (4).
Those who absorbed lead have been storing it in their bones, and reabsorbing it every now and again. Lead can
been stored in the bones for decades and when it is reabsorbed into the bloodstream then it travels to all of the
organs once again and damages them (2). Bones release all of the minerals that they store at different rates of
time, and the distribution of lead throughout the skeleton is not uniform. Therefore it is proposed that some of
the lead stored in the bones isn’t available for immediate reabsorption into the body (4). Differences in age and
gender will also affect someone’s blood level. A female is likely to have a 20-30% lower blood lead level than a
male of the same age (1). It has also been documented that as a person ages this rate gradually slows down and
then slightly increases around 60 years (4).
There is an ambiguity between the bone and blood lead levels. It has always been believed that from its intake
lead is either in the blood traveling between all of the soft tissues, being deposited into the bones, or being
removed from the body via urine of feces (4). However some would argue that there is a difference because
different types of bone have different turnover rates. This means that the amount of lead found in the bone
depends on the metabolism of type of bone being examined (6).
Bone and blood lead levels are related. Lead levels in the bones should be monitored to identify certain
individuals are at risk for elevated blood lead levels in the future (5). It can be hypothesized that if the amount of
lead stored in the bones is large and the turnover rate of the bone is fast, that more lead will be present in the
blood. The author suggests that a chronic exposure to lead would be more harmful than a short very high blood
level for an individual (4). A correlation has also been shown between people with high levels of lead stored in
their bones and high blood pressure, slowed reaction time, worsened memory and the inability to learn new
information (2).
Throop vs. Moosic
It has been hypothesized that cumulative lead exposure is more harmful that a
single high dosage. There are still some people living in very contaminated areas. A
study was conducted comparing two Pennsylvanian towns. One of these towns Throop
was located just one mile away from a factory, which use to be a car battery recycling
plant, and was later converted to a lead smelter which was active until 1981. The other
town is located in beyond the valley and out of similar wind patterns, which is expected
to prevent any airborne particles from reaching it. The participants in the study were
grouped based on age, because it is thought that bone metabolism slows with age. The
participants underwent both a blood test to calculate the blood lead levels and an x-ray
fluorescence test to find the bone lead levels. It was shown that those living in the town
without the unusual lead exposure, Moosic, had a lead level that was acceptable with
the norm of the rest of American. Those who were living in Throop however had
elevated levels. It is proposed that the nearness of the factory contaminates the all
surrounding soil and dust, especially that which will reach residential homes.
Examination of the surrounding areas showed that the lead concentration in the soil
was 200-1900 times higher than the concentration found elsewhere in the same
county.