Perchlorate in the United States. Analysis of Relative Source Contributions to the Food Chain

Perchlorate has been considered by some a potential
threat to human health, especially to developing infants
and children because it may inhibit iodide uptake by the
sodium iodide symporter (NIS) of the thyroid. In the United
States, during the last several decades, environmental
perchlorate has had three recognized sources stemming
from (a) its use as an oxidizer (including in rocket propellants),
(b) its presence in Chilean nitrate fertilizer (CNF), and (c)
natural production. An analysis of the relative source strengths
and how they may influence entry into the food chain
has not been conducted. Averaged over the last ∼60 years,
we estimate that the source strengths have been (a)
10.6, (b) 0.75, and (c) 0.13−0.64 Gg/y for the United States
as a whole. Of this, while (b) and (c) represent actual
dispersed amounts, the figure in (a) is the amount
of perchlorate produced and only a fraction (f) of it has
been dispersed and often in a more localized fashion. In
addition, dispersal of (b) has taken place only over agricultural
land. Considering that the total land area in the United
States is 5.5× the arable land area, in terms of incorporation
into the food chain, the figure cited in (b) has a proportionately
greater impact. Most estimates of f will thus suggest
that over the considered period, the contribution of CNF
to incorporation of perchlorate in the food chain has likely
been comparable to oxidizer perchlorate, with natural
production being a lesser source. Fireworks presently
constitute a potentially important source of increasing
importance but a quantitative impact cannot yet be assessed.