Hi Mohammed, you can only derive a protein concentration from a competitive ELISA under very special circumstances. If you are not sure whether you have these conditions in your experiment you should work with IC50 values.
About Lead-Based Paint. Lead is a highly toxic metal that may cause a range of health problems, especially in young children. When lead is absorbed into the body, it can cause damage to the brain and other vital organs, like the kidneys, nerves and blood. Lead may also cause behavioral problems, learning disabilities, seizures and in extreme cases, death.
In more modern times, the durability of lead made it an excellent paint additive, but the sweetness made it tempting to young children. Childhood lead poisoning was linked to lead-based paints in 1904. Several European countries banned the use of interior lead-based paints in 1909. At one time baby cribs were painted with lead-based paint, which resulted in infant illness and death.