Don’t eat the dust! Let’s assume that a 2 year old child visits a residential en

Question

Don’t eat the dust!

Let’s assume that a 2 year old child visits a residential environment which contains soil and dust containing 0.5% lead by weight for one month (30 days). Let’s also assume that

Lead stays in the bloodstream for 40 days (more than the entire month of exposure).

The child absorbs 40% of ingested lead and 1% of the absorbed lead makes into the blood.   

The average density of whole blood for a human is about 1060 kg/m3.

The average2 year old girl weighs 12 kg.  

The human body contains about 7% blood by weight. Dust consumption rates for children are provided in the table above.

a)Calculate the blood lead level in the child in g/dl  (Note: dl is deciliter).

b)Calculate the percent of Pb in the blood on a mass basis.

TABLE 1-IEUBK Soil/Dust Ingestion Defaults by Age Age Group (years IEUBK Model Defaults (g/day) 0-1 1-2 2-3 3-4 4-5 5-6 6-7 Source: U.S. EPA, 1994 0.085 0.135 0.135 0.135 0.100 0.090 0.085

Explanation / Answer

The solution can be divided into the following segments to arrive at the final answer –

1. Total amount of dust consumed –

According to table, the 2 year consumes 0.135 grams dust/soil per day

Therefore, dust consumed in 30 days = (30 * 0.135) = 4.05 grams.

2. Amount of Lead (Pb) consumed-

According to data, Pb is present in 0.5% w/w in soil/dust = (0.5gms Pb in 100gms of soil/dust)

Therefore, amount of Pb in 4.05gms soil/dust = (4.05 * 0.5) / (100) = 0.02gms

The child has consumed 0.02gms Pb in 30 days.

3. Amount of Pb absorbed –

The child is able to absorb 40% of consumed Pb.

Therefore, 40% of 0.02 = 0.008gms of Pb absorbed by the body

4. Amount of Pb that makes it to the blood stream

According to data, 1% of absorbed Pb makes it blood stream.

This means, 1% of 0.008 = 0.00008gms of Pb is present in the blood of the child

5. Amount of blood in the child’s body –

According to data, amount of blood = 7% of body weight

Body weight = 12Kg

Therefore, amount of blood = 7% of 12 = 0.84Kg

6. Volume of blood in the body –

The density (D) of blood = 1060Kg / 1m3 = 1060 Kg/1000 Liters

That means, 1000 liters will have 1060Kg of blood.

The child contains 0.84Kg of blood.

Therefore, the volume of blood in the child = (0.84 * 1000) / (1060) = 0.792Liters

7. Analysis of above data –

The child Pb levels are as follows –

0.00008gms Pb in 0.84Kg of Blood
0.00008gms Pb in 0.792L of Blood

Solution A –

1 deciliter = 0.1L

Using data from point 7, the blood lead level in g/dL = 0.000008 grams / 1 deciliter

Solution B –

Percent of Pb in the blood on a mass basis = (0.00008 gms / 840gms) * 100 = 0.0000095% = (9.5 * 10-6) %

0.00008gms Pb in 0.84Kg of Blood
0.00008gms Pb in 0.792L of Blood

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