Correspondence on: Household use of crop residues and fuelwood for cooking and newborn birth size in rural Bangladesh by Lee et al

The study by MiSun Lee and colleagues has investigated the risk of adverse outcomes in offspring on perinatal exposure to cooking biomass fuels in Bangladeshi women, particularly crop residue and woodfuel, and reported an increased odds of low birth weight and a significant reduction in the gestational age and head circumference of offspring on exposure to smoke from crop residue burning. While it is an insightful effort carried out among a considerable cohort of 1137 participants, the quantification of exposure using only a questionnaire tool may have potentially obscured the estimation of the actual exposure and the overall effect size. Despite several epidemiological factors are accounted for, no information pertaining to the quality of antenatal care, including diet or nutrition during gestation and preexisting and/or pregnancyassociated comorbid conditions of the participating women have been recorded or included in the analyses such as hypertension, preeclampsia, diabetes and other metabolic conditions, which are most important and could possibly confound the association. Moreover, besides the information on the type of cooking fuel and secondhand smoke, other environmental exposures could have been recorded such as the air pollution or PM2.5 levels, given that the two clinics from which the participants have been recruited are in the same region. Also, any identifiable difference in infant sexbased birth outcomes could have been a telling observation. Adverse birth outcomes are infelicitous occurrences and continue to remain a major public health challenge in lowincome and middleincome countries, including India. Several measures have been taken in the past decades to ameliorate the factors, especially related to strengthening of the health system for providing improved service provisions and effective care to women during gestation. However, the environmental components of exposure are difficult to investigate, often overlooked and need accelerated attention for research and control. In India and few other regions of the world, community practices such as increased burning of crop residue or stubble at home for cooking and in agricultural lands are common, leading to escalated levels of toxic chemical laced smoke in both indoor and outdoor environment, which affects the population health, especially pregnant women and children are highly vulnerable. While the authors discuss that the greater effect of crop residue is not fully explainable and highlight a few potential mechanisms of action towards increasing the risk of adverse outcomes in offspring such as the effects of PM2.5 and polycyclic aromatic hydrocarbons released during burning, no attention has been given to the crucial exposure to pesticides and insecticides, along with other industrially manufactured chemicals such as phthalates, bisphenol A, polychlorinated biphenyls and perfluoroalkyl and polyfluoroalkyl substances, which are known hormonemimicking, endocrine and immunomodulatory agents. These are deliberately added as plasticiser formulations in fertilisers, pesticides and insecticides, are unregulated, and indiscriminately used in agricultural lands and on crop produce for increasing yield and pest control. Several examples of unintended chemical exposures are well known such as the introduction of organochlorine insecticides in the 1950s and dichlorodiphenyl trichloroethane used for agricultural control of pests, which were later observed to be genotoxic, and having mutagenic effects, perturbing the hypothalamus– pituitary–thyroid axis, causing birth defects and other developmental abnormalities in offspring. Evidence from several epidemiologic and experimental studies clearly support that these chemicals are toxic and can modulate the endocrine signalling in humans, leading to pathophysiological dysfunction with risk of adverse birth outcomes, including abnormal newborn telomere length and other chronic diseases such as breast cancer, with potential to alter the epigenetic tagging, leading to trans and intergenerational effects. Therefore, the observed strong association of crop residue and adverse outcomes in offspring in this study could be the resultant harmful effects of toxic chemical mixtures including plasticisers in the emissions from crop residues, which are causing sustained everyday exposure by potentially bioaccumulating and biomagnifying in different tissue and organs within the body. It would have been intriguing to observe if any biological specimen such as blood or urine of mother and/or foetal cord blood during first trimesters could have been collected during enrolment and screened for the presence of chemical markers and correlated to see if the association stands. The burning of crop residues containing chemical formulations at home for cooking and in agricultural fields for increased yield and pest control has been a major global health concern for decades, which should be of high priority for awareness and advocacy, so as to reduce the severe detrimental effects on maternal and child health, associated with sustained pervasive exposure to these chemicals. Populationlevel interventions through policy limiting use of these chemicals in agricultural fields, banning stubble burning and providing better solutions for its management and reducing indoor exposure to biomass pollutants through promotion and availability of cleaner fuel sources in such rural populations could help reduce increased risk.