Dilution or concentration of applied toxics can be anticipated,
depending on the size of the treated area. Fugacity modeling
[72] predicts that the amount of pesticides remaining in
small agricultural units is reduced in comparison with larger
production areas even if the same agronomic receipts (pesticide
loads/unit land surface) were applied in both cases. This is
because the perimeter/area relation decreases nonproportionally
to a reduction in area. Air advection occurs through some
part of the field perimeter (; 1/4 at a time), and the minimum
perimeter to area ratio in 5-ha fields is 1.6E22 as compared
with 4.42E24 in 400-ha fields. Assuming a mixing air mass
with a height at about 1,000 m, the residence times of advective
air are 2.0E23 d and 1.8E22 d at the smaller and larger fields,
respectively. The faster turnover of clean air from outside
through the smaller areas results in lower pollutant exposures.
Similar reasoning can be applied to water advective flows.
Fugacity estimates corresponding to several pesticides used in
citrus crops of Misiones province (Argentina) [73] predict
nearly 10-fold reductions of pesticide concentrations in soils
and waters and human exposure risks at typical 5-ha crops as
compared with 400-ha crops with the same management system
(Fig. 3).