The aim of this study was to determine reliable measures of fetal exposure to environmental pesticides. A few studies have reported on the analysis of cord blood or meconium for pesticides. Cord blood was analyzed together with maternal blood to monitor chlorpyrifos, diazinon and propoxur exposure during pregnancy (16
). Meconium was analyzed for organophosphates (18
), DDE (19
), organochlorines (20
) and various pesticides (21
). However, this is the first report to analyze cord blood, infant hair and meconium samples together to determine the most sensitive matrix to detect antenatal pesticide exposure. Our results show that meconium is, by far, the best matrix for this purpose. Of the eleven pesticides that were analyzed, eight were detected in meconium and for propoxur, the frequency of exposure was 23.8%. In contrast, cord blood and infant hair were each only positive for a single pesticide, propoxur and chlorpyrifos, respectively. We did not analyze infant urine due to inherent problems and difficulty associated with urine collection in infants, compared to cord blood collection. Furthermore, there are inherent problems associated with the interpretation of urine results, particularly if only spot samples were collected (28
). We also felt that cord blood represented an appropriate matrix to analyze for exposure to pesticides particularly because parent pesticides can be detected in the blood in contrast to urine (28
The high rate of detection of pesticides in meconium is consistent with the reported high sensitivity of meconium for the detection of other xenobiotics including illicit drugs, licit drugs, nicotine metabolites and alcohol metabolites (29
). This is a consequence of the repository nature of meconium for xenobiotics which facilitates the measurement of a wide window of exposure. Meconium is formed early in gestation and most xenobiotics that the fetus is exposed to during gestation are deposited in meconium, through fetal swallowing and/or bile secretion up to the time of birth (30
). Since meconium, unlike fetal urine, is not normally excreted in utero, xenobiotics deposited in meconium accumulate and increase in concentration which further enhances the likelihood of their detection.
In contrast, pesticides in cord blood represent acute exposure and may not be readily detected due to their low concentrations in the blood as a result of the metabolism, excretion and deposition in tissues of the pesticides. Due to the transient state of pesticides in blood, compared to meconium, blood is not an adequate matrix to measure cumulative exposure. A highly sensitive technique to detect pesticides in blood has been published with LOD’s three orders of magnitude lower than our levels. However, the specificity of such a method is compromised since in many instances, only a single mass ion, which is not the molecular ion, was used for compound identity. The authors acknowledge that lowering the LOD, in effect, was associated with an imprecision that was about double those with higher detection limits (31
). On the other hand, for this study, we used more stringent criteria for compound identity including appropriate retention time based on positive controls and the presence in the mass spectra of specific mass and qualifier ions as well as appropriate mass/qualifier ion ratios. Our strict criteria may have decreased the sensitivity of the method but has retained the high specificity of the GCMS method.
We did not detect any pesticide in infant hair except in one sample that was positive for chlorpyrifos. It appears that the deposition of pesticides in infant hair does not occur as readily compared to other compounds such as illicit drugs, nicotine, and most recently, fatty acid ethyl esters (32
). The pharmacokinetics and tissue distribution of pesticides in the fetus is largely unknown. The metabolism of pesticides is low due to the poor detoxification mechanisms (2
). Furthermore, fetal hair starts to grow at approximately six to seven months of gestation (32
) so that the timing of maternal exposure during pregnancy could also influence incorporation of pesticides into the growing hair shaft. It is also likely that due to the small amount of hair that could be collected from the newborn infant, the limited amount of the sample for analysis prevented the detection of minute quantities of pesticides in infant’s hair. In contrast, our results with infant hair analysis differ remarkably with maternal hair which we found to be a better matrix to analyze for pesticides compared to maternal blood (24
). In part, this difference may be secondary to more hair sample that could be obtained from the mother for analysis compared to newborn hair. Thus, infant hair is not ideal for the analysis of pesticides due principally to the low concentration of the pesticides and the limited amount of hair that could be collected from the subjects. Furthermore, although pesticide metabolites may deposit in hair, it has also been found that the metabolites tend to partition predominantly towards blood rather than into hair (34
Almost no pesticide metabolites were detected in the present study in all of the matrices that were analyzed. A number of workers who have studied pesticide metabolite in meconium have found DDE (19
) and organophosphate metabolites (18
). Hong et al (19
) randomly sampled 60 meconium samples in Germany and detected DDE in 3 of them. However, the pesticide metabolite concentration that they detected was 11.1 ng/g, which is lower than our LOD for DDE. Our method had a higher LOD since it was optimized to detect many classes of metabolites, especially the pyrethroids, whereas Hong and colleagues were selectively searching for DDE. However, we did find one meconium sample positive for DDE. Whyatt & Barr (18
) found diethylthiophosphate (DETP), an organophosphate metabolite, in 100% of meconium samples studied in New York. We attempted to analyze for this compound using our current meconium liquid-liquid extraction method. However, it was discontinued due to difficulty in the chromatographic separation of DETP from TCP. The survey had reported higher use of malathion and chlorpyrifos, for which we had specific metabolites that we could accurately measure, than for diazinon, for which DETP would be a potential metabolite.
Pesticides that partition and accumulate in adipose tissues such as organochlorines may not be found in sufficient concentrations in blood, urine or meconium. Although DDT was found in meconium, the frequency of detection was low (0.6%). The use therefore of cord blood, infant hair and meconium as matrices for the detection of fetal exposure to these compounds is a recognized limitation of the study. However, access to fetal or infant adipose tissue is normally not feasible; thus its diagnostic use in clinical settings may not be practical. On the other hand, failure to detect lipophilic pesticides from the analysis of non-adipose tissue matrices should not imply non-exposure to these types of pesticides.
Overall, this study has shown that exposure to home pesticides constituted a high exposure risk among pregnant women even in an agricultural setting such as in our study. This observation parallels the reports which have shown a high exposure rate to home pesticides among pregnant women and their infants residing in urban areas (16
). It is therefore evident that whether in city or rural areas, pesticides that are used at home pose a very high exposure risk among pregnant women and can be related to a number of factors such as a widespread and inappropriate use of pesticides at home. Due to a high number of pests (flies, mosquitoes and roaches) in the homes of the subjects, spray pesticides are commonly used (43%), principally Baygon™
(90%) which contains propoxur and cyfluthrin. Inappropriate use of these home pesticides was evident since 38.2% of the spraying was done by the pregnant woman and reentry time to the sprayed area was ≤ 60 minutes in 75% of the cases. Inadequate labeling on the safe use of the pesticide may be a major reason for its improper use. Labels do not warn that the product should not be used by the pregnant woman, nor explicitly instruct on the appropriate reentry time of the sprayed area. Corrective measures to prevent further pesticide exposure have been instituted as a result of our findings. Assessment of the clinical outcome in the child of prenatal and ongoing exposure to pesticides is also under way.
In conclusion, our study has demonstrated that compared to cord blood or infant hair, meconim is the most sensitive matrix to analyze for fetal exposure to pesticides. The accumulation of pesticides in meconium, the ease of meconium collection and the large amount of sample that could be obtained for analysis are all factors that contribute to the increased sensitivity of this matrix.