Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:13:p3
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 13 (pt 3/9)
Character Range: 2315383–2318254

of soil. While likely to be negligible, potential inhalation exposures associated with dust have been considered in the HIL derived.

    13.3.4     Plant Uptake
An important aspect of the potential for plant uptake of zinc is the potential for zinc to be present in soil water. The concentration of zinc in soil solution is dependent on the form and amount of zinc present in the soil, solubility of the particular zinc compound, and the extent of adsorption. Zinc compounds vary significantly in solubility (CCME 1999).

Geochemical differences in zinc concentrations in soil and autonomic selection processes during the evolution of plants result in a great variation in zinc demand and zinc content between plant species and between plant genotypes of the same species. As a general rule, plants from environments poor in zinc are characterised by low zinc concentrations, those from zinc-enriched environments by high concentrations (WHO 2001).

Zinc toxicity to plants affects general physiological processes, e.g. transpiration, respiration and photosynthesis, and plant development in general can be visibly inhibited. The critical leaf tissue concentration of zinc at which growth is affected was found for many plant species to be between 200 and 300 mg/kg dry matter (WHO 2001). However, zinc phytotoxicity in leaves can depend to a large extent on the plant species, the age of the leaf and other factors such as exposure period and exposure concentration.

An extensive literature review of plant uptake of zinc has not been undertaken, and few quantitative values are available that are specifically relevant to different types of edible produce, but the potential for plant uptake has been considered in the derivation of the HIL A. The approach adopted by MfE (2011) in the derivation of a soil guideline where plant phytotoxicity may be of importance has been adopted in the derivation of an HIL. This approach considered potential intakes associated with consumption of home-grown produce in soil concentrations that are not phytotoxic (based on the lower limit of phytotoxicity) as part of the overall intake from other sources.

For zinc, plant growth is considered to be affected at concentrations between 200300 mg/kg tissue concentration. To estimate the additional background intake, a child's produce consumption (0.048 kg DW[3]/day) was multiplied by 200300 mg/kg and divided by the child body weight of 15.5 kg to obtain the maximum additional background daily intake for 100 % of produce being home-grown. For the consumption of 10% home-grown produce this results in an additional intake of 0.06 to 0.09 mg/kg/day was considered.

It is noted that the inclusion of home-grown produce in the calculations presented for HIL A results in some double counting of intakes from fruit and vegetable produce. The amount of double counting cannot be