Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:13:p1
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 13 (pt 1/9)
Character Range: 2310090–2312950

13             Zinc

13.1          General
Several comprehensive reviews of zinc in the environment and its toxicity to humans are available and should be consulted for more detailed information not presented in this summary (ATSDR 2005; WHO 2001; NEHF 1997). The following provides a summary of the key aspects of zinc that are relevant to the derivation of a soil HIL.

Zinc is ubiquitous in the environment and occurs in the Earth's crust at an average concentration of about 70 mg/kg. Zinc is not found in elemental form in nature, and occurs in the +2 oxidation state primarily as various minerals such as sphalerite (zinc sulfide), smithsonite (zinc carbonate), and zincite (zinc oxide). Fifty-five zinc-containing minerals are known to exist. In its pure elemental (or metallic) form, zinc is a bluish-white shiny metal (WHO 2001).

Most rocks and many minerals contain zinc in varying amounts. Commercially, sphalerite (ZnS) is the most important ore mineral and the principal source of the metal for the zinc industry (WHO 2001). Inorganic zinc salts have numerous commercial uses. Zinc oxide is used in the rubber industry as a vulcanisation activator and accelerator and to slow down oxidation, and also as a reinforcing agent, heat conductor, pigment, UV stabiliser, supplement in animal feeds and fertilisers, catalyst, chemical intermediate, and mildew inhibitor. Zinc sulfate is used in rayon manufacture, agriculture, zinc plating, and as a chemical intermediate and mordant. Zinc chloride is used in smoke bombs, in cements for metals, in wood preservatives, in flux for soldering, in the manufacture of parchment paper, artificial silk, and glues, as a mordant in printing and dye textiles, and as a deodorant, antiseptic and astringent. Zinc chromate is used as a pigment in paints, varnishes, and oil colours. In addition, zinc phosphide is used as a rodenticide while zinc cyanide is used in electroplating.

Zinc is an essential element for all living things, including man. Zinc-containing proteins and enzymes are involved in every aspect of metabolism, including the replication and translation of genetic material.  Hence adverse effects are associated with deficiency and toxicity associated with excess intake. Zinc deficiency has been reported to affect children of many countries while other groups identified at particular risk are women of child-bearing age and the elderly. The main cause of human zinc deficiency is consumption of diets that contain little highly bioavailable zinc (NEHF 1997).

13.2          Previous HIL
The derivation of the previous HIL (HIL A = 7000 mg/kg) for zinc is presented by Imray & Neville (1996). In summary, the HIL was derived on the basis of the following:
    * Based on data from the US, background intakes for adults were estimated to be 0.23 mg/kg/day, 77% of the adopted threshold TDI of