Human Exposure Pathways - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 464

In most countries, statistics are available of the total vegetable consumption
rate and the consumption pattern, although these statistics often are outdated. As
mentioned in Section 11.2.2.3 , it does not always make sense to relate a vegetable(-
group)-consumption-rate-weighed BCF to the vegetables that are actually grown at
the site. The reason for this is that this vegetable pattern does not represent a sus-
tainable situation, i.e., the type of vegetables might change the next several years.
In most cases it is more useful to consider the risks from the consumption of veg-
etables produced over a longer time span, where consumption is represented by an
average vegetable package for the country or region. An exception could be made
when there is a tradition of producing a specific vegetable on the contaminated site,
because of either local conditions or regional traditions. In this case, a site-specific
or region-specific food package could be assessed, or the general country-specific
vegetable consumption statistics could be adapted to the regional conditions. In both
cases, the result is a specific BCF for the site or region, as the basis of a “regional”
vegetable group-consumption-rate-weighing.
In a screening Risk Assessment, it is possible to focus on vegetables that have a
high uptake affinity for the contaminant. When human health risk can be excluded,
the Risk Assessment is then concluded. When risks cannot be excluded, more real-
istic vegetable consumption patterns have to be considered in subsequent stages of
the Risk Assessment.

11.2.4.2 Fraction of Vegetables that is Home-Grown

In the majority of countries, the fraction of vegetables that is home-grown,
f home-grown , is not specified for each vegetable separately. In most countries, no
decent statistics on this fraction exist. Besides, this fraction will differ between
regions and between cities and rural areas. An exception are the detailed statistics
on the fraction of vegetables that is home-grown for France (INSEE 1991 ). These
fractions are given on the scale of six different regions. Generally, the specification
of the fraction of vegetables that is home-grown is partly a judgement, or a policy
decision. In the Netherlands, as an example, the following default data are used for
this fraction for groups of vegetables, depending on land use:

• “Residential site, with garden”: 10% for all vegetables;

• “Vegetable garden”: 50% for potatoes and 100% for other vegetables.

The differentiation of the fraction of vegetables that is home-grown between
potatoes and other vegetables for the land use “Vegetable garden” is made because
it is not realistic to use a value of 100% for potatoes. Because the consumption
rate of potatoes is rather high, an exceptionally large vegetable garden would be
needed to provide all the potatoes required. These values reflect the policy decision
made in the Netherlands that: “the soil quality must offer the possibility of consum-
ing at least a specified percentage of home-grown vegetables”. Since the exposure
to contaminants is sensitive to the fraction of vegetables that is home-grown,