The mechanism by which a toxic material gains entry into the body depends on the form of the substance
For instance, lead solder is not hazardous in its solid form because it cannot enter the body. While soldering, the lead turns into liquid form and there are chances of it coming in contact with the skin. When the spilled liquid solidifies, it may turn into small particles of dust that can be inhaled or ingested.
Also, fumes may be generated when lead is heated to very high temperatures and these fumes are extremely hazardous as they are absorbed and inhaled easily. Therefore, most toxic substances in solid form are not hazardous unless they present as tiny particles (dust).
Some hazardous substances may be present in liquid form, which can be absorbed through the skin. Liquids may evaporate and form gases, which can be inhaled. The size of the fiber also decides the degree of damage it causes.
Tiny fibers of asbestos can lodge in the lungs causing serious problems. Spraying pesticides and machining of metals can create mists, which when inhaled can be toxic.