Pyrethroids in human breast milk: Occurrence and nursing daily intake estimation
Highlights
► Analysis of human breast milk showed the presence of pyrethroids in 100% of the samples. ► Concentration levels of pyrethroids were up to 25 ng g− 1 lw. ► An exponential decay was observed when pyrethroid concentration was confronted against parity. ► The estimated daily intakes for nursing infants were always below the acceptable daily intake levels.
Introduction
Pyrethrins are natural insecticides produced by certain species of chrysanthemum such as Chrysantemum cinerariaefolium. Chemically, they are ethers from chrysanthemic acid. In order to increase their stability in the environment, some different derivates have been synthesized. These semi-synthetic compounds are named pyrethroids. Their success as pesticides is due to its neurological toxicity slowing the kinetics of sodium channels in the neuronal membranes. Structurally, there are two types of pyrethroids: type II with a cyanic group in position α respect the carboxylic group, and type I without it (Gosselin, 1984).
These pesticides had been intensively used for malaria and dengue control against Aedes spp., among other vector mosquito species. But these mosquitoes developed resistance to pyrethroids (Lima et al., 2011). For instance, in Brazil in 1999, pyrethroids were introduced to replace organophosphate insecticides such as temephos and malathion. However, three years later there was evidence of resistance against cypermethrin (da-Cunha et al., 2005).
Pyrethroids contain 2–3 chiral centers depending on their structure, so each pyrethroid could contain 2 or 4 enantiomer pairs and different diastereoisomers. They are hydrophobic compounds with log octanol–water partition coefficient (Kow) values near to 6 (Feo et al., 2010a) and their environmental persistence uses to be short (between 12 and 197 days) (Feo et al., 2010b). Nevertheless, since in the last decades the usage of pyrethroids has increased widely in the indoor as household insecticides, insect-control products, pet shampoos and lice treatments, and in the outdoor as agricultural pesticides and for pest control, they are almost ubiquitous and, as long as they are dumped continuously, they will be always present in the environment.
One of the most important aspects in pollutant studies is the toxicity of the compound on non-target organism. For pyrethroids, they are known to have high toxicity in fish (San Francisco Estuary Project, 2003). However, in mammals it is unclear but it seems that they have carcinogenic and endocrine disrupting effects (Cox, 1996, George et al., 2011, Liua et al., 2011). Toxicity in humans was expected to be low because pyrethroids are converted to non-toxic metabolites, such as phenoxybenzoic acid, by hydrolysis in mammals (Chambers, 1980, Demoute, 1989, Godin et al., 2007). That explains why most of pyrethroid exposure studies are based on the analysis of this metabolite in urine samples. Contrary to this assumption, in 2001, Zehringer and Herrmann found pyrethroids in human breast milk in urban Swiss population. Other recent works have also shown the bioaccumulation of pyrethroids in human breast milk, with levels up to 2000 ng g− 1 lw (Sereda et al., 2009, Feo et al., 2012). These studies were carried out with population from areas in which pyrethroids were mostly applied as insecticides in agriculture, domestic use and for malaria control. However, there are very few works reporting pyrethroid levels in human breast milk.
The objective of this work is to study the presence of 13 different pyrethroids in human breast milk samples collected from different countries in Europe (Spain) and South-America (Brazil and Colombia), including urban and rural areas where different pyrethroids are used. Fifty six human milk samples were collected and analyzed by GC–MS–MS, for the determination of concentration levels of pyrethroids as well as their isomeric composition.
Section snippets
Study areas
Twenty human breast milk samples from Brazil, 27 from Colombia and 6 from Spain were collected. Samples coming from Brazil corresponded to two different zones: São Paulo (urban), a big city with an associated large metropolitan area, and Rondônia (rural), a state near to Amazon. All samples collected during 2009 and 2010 were individual samples. Moreover, three additional samples were included in the study, corresponding to archived pools of different individuals: pool 1, a pool of 10
Pyrethroid levels in human breast milk
Basic statistics of pyrethroid levels found in breast milk samples are reported in Table 3. Each batch of samples analyzed together included one procedure blank. None of those showed levels with upper LOQ for any analyte. Pyrethroids were detected in all the human milk samples analyzed, at concentration levels ranging between 1.45 and 24.2 ng g− 1 lw. Similar total results were obtained for the three different countries. Results from the urban Spanish area (mean value of 4.89 ng g− 1 lw) were very
Conclusions
In view of the present study, pyrethroids seem to be ubiquitous contaminants in human breast milk samples. This could point out their potential for bioaccumulation, contradicting the assumption that all pyrethroids are metabolized by hydrolysis in mammals. Their presence is not just restricted to those cases in which pyrethroids were applied for malaria or dengue control, but also is reflected in samples collected in areas where pyrethroid use is reduced to agricultural and domestic
Acknowledgments
We thank all the women for their participation in the study. We also thank Alexandra Jelic for their assistance in revising the manuscript. This research work was funded by the Spanish Ministry of Economy and Competitiveness through the project CEMAGUA (CGL2007-64551/HID).
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