There is an assumption that
pyrethroid pesticides are converted to non-toxic metabolites by hydrolysis in mammals. However, some recent works have shown their bioaccumulation in human breast milk collected in areas where
pyrethroids have been widely used for agriculture or
malaria control. In this work, thirteen
pyrethroids have been studied in human breast milk samples coming from areas without
pyrethroid use for
malaria control, such as Brazil, Colombia and Spain. The concentrations of
pyrethroids ranged from 1.45 to 24.2 ng g⁻¹ lw.
Cypermethrin, λ-
cyhalothrin,
permethrin and
esfenvalerate/
fenvalerate were present in all the studied samples. The composition of
pyrethroid mixture depended on the country of origin of the samples,
bifenthrin being the most abundant in Brazilian samples, λ-
cyhalothrin in Colombian and
permethrin in Spanish ones. When the
pyrethroid concentrations were confronted against the number of gestations, an exponential decay was observed. Moreover, a time trend study was carried out in Brazil, where additional archived pool samples were analyzed, corresponding to years when
pyrethroids were applied for
dengue epidemic control. In these cases, total
pyrethroid levels reached up to 128 ng g⁻¹ lw, and concentrations decreased when massive use was not allowed. Finally, daily intake estimation of nursing infants was calculated in each country and compared to acceptable WHO levels. The estimated daily intakes for nursing infants were always below the acceptable daily intake levels, nevertheless in certain samples the detected concentrations were very close to the maximum acceptable levels.