Assessing Effects of Genetically Modified Plant Material on the Aquatic Environment Using higher-tier Studies.

Genetically modified organisms are used extensively in agriculture. To assess potential side effects of genetically modified (GM) plant material on aquatic ecosystems, only a very small number of higher-tier studies have been performed. At the same time, these studies are particularly important for comprehensive risk assessment covering complex ecological relationships. Here we evaluate the methods of experimental higher-tier effect studies with GM plant material (or Bt toxin) in comparison to those well-established for pesticides. A major difference is that nominal test concentrations and thus dose-response relationships cannot easily be produced with GM plant material. Another important difference, particularly to non-systemic pesticides, is that aquatic organisms are exposed to GM plant material primarily through their feed. These and further differences in test requirements, compared with pesticides, call for a standardisation for GM-specific higher-tier study designs to assess their potentially complex effects in the aquatic ecosystems comprehensively.

The Ecotoxicology of Microbial Insecticides and Their Toxins in Genetically Modified Crops: An Overview.

The use of microbial insecticides and their toxins in biological control and transgenic plants has increased their presence in the environment. Although they are natural products, the main concerns are related to the potential impacts on the environment and human health. Several assays have been performed worldwide to investigate the toxicity or adverse effects of these microbial products or their individual toxins. This overview examines the published data concerning the knowledge obtained about the ecotoxicity and environmental risks of these natural pesticides. The data presented show that many results are difficult to compare due to the diversity of measurement units used in the different research data. Even so, the products and toxins tested present low toxicity and low risk when compared to the concentrations used for pesticide purposes. Complementary studies should be carried out to assess possible effects on human health.

Biochemical analyses demonstrate that Bt maize has no adverse effects on Eisenia fetida.

The potential effects of Bt (Bacillus thuringiensis) maize on non-target organisms should be evaluated before such maize is commercially planted. Earthworms play an indispensable role in the soil ecosystem; act as important bio-indicators of soil quality and environmental pollution. Therefore, earthworms are often used as the object to evaluate the non-target effect of Bt maize. To accelerate the commercialization of transgenic maize in China, a 90-day Eisenia fetida feeding experiment was conducted to evaluate the potential effects of Bt maize line, BT799-which was developed by China Agricultural University and contains the Cry1Ac gene-and its non-Bt conventional isoline-Zheng 58-on E. fetida. Our results showed that the Bt maize line had no significant effects on the growth, reproduction, or enzymatic activities of these earthworms. In summary, Bt maize had no toxic effects on E. fetida.

Safety assessment of phytase transgenic maize 11TPY050 in Sprague-Dawley rats by 90-day feeding study.

The present study aimed to evaluate the subchronic toxicity of feeding with phytase-transgenic maize line 11TPY050 in Sprague-Dawley (SD) rats. Rats (n = 10/sex/group) were fed with 12.5%, 25% or 50% (w/w) transgenic maize diet, 12.5%, 25% or 50% (w/w) non-transgenic isoline OSL940 maize diet, or 50% (w/w) commercially available Zhengdan958 maize diet for 90 days. Daily clinical observations and weekly measurements of body weights and food consumption were conducted. Blood samples were collected on day 46 and day 91 for hematology and clinical chemistry evaluations. At the end of the study, macroscopic and microscopic examinations were performed. No effects on body weight and food consumption were observed. The results of hematology, clinical chemistry, and absolute and relative organ weights in the transgenic maize group were comparable to those in the parental maize group. Several statistical differences were not dose-related and were not considered to be biologically significant. Furthermore, the terminal necropsy and histopathological examination showed no treatment-related changes among the groups. The results from the present 90-day feeding study of phytase-transgenic maize 11TPY050 indicated no unexpected adverse effects in SD rats. The phytase transgenic maize 11TPY050 has substantial equivalence with non-transgenic maize.

Performance of Daphnia magna on flour, leaves, and pollen from different maize lines: Implications for risk assessment of genetically engineered crops.

Non-target effects of genetically engineered (GE) plants on aquatic Daphnia magna have been studied by feeding the species with different maize materials containing insecticidal Cry proteins from Bacillus thuringiensis (Bt). The results of those studies were often difficult to interpret, because only one GE plant was compared to one related non-GE control. In such a setting, effects of the Cry proteins cannot be distinguished from plant background effects, in particular when the test species is nutritionally stressed. In the present study, we tested the suitability of three different maize materials, i.e., flour, leaves and pollen, from five diverse non-GE maize lines (including EXP 258, a breeding line that is closely related to a SmartStax Bt maize) as exclusive food sources for D. magna. The parameters recorded included survival, sublethal endpoints such as body size, number of moltings to first offspring, time to first offspring, number of individuals in first clutch, total number of clutches, total number of offspring, average number of offspring per clutch, and population measures such as net reproductive rate R0, generation time T and intrinsic rate of increase rm. The results showed that D. magna can survive, grow and reproduce when fed only maize materials, although the performance was poorer than when fed algae, which indicates nutritional stress. Large differences in life table and population parameters of D. magna were observed among the different maize lines. Our results suggest that confounding effects caused by nutritional stress and plant background might explain some of the conflicting results previously published on the effects of Bt crops on D. magna. Using 95% confidence intervals for the means of the five maize lines for all measured parameters of D. magna performance in our study, we captured the natural range of variation. This information is useful for the interpretation of observed differences in D. magna performance between a GE plant and its non-GE comparator as it helps judging whether observed effects are of biological relevance. If differences between a GE and comparator line are observed and their biological relevance needs to be assessed in future risk assessments of GE maize, 1) the data on natural variation of the different parameters generated by previous studies can be informative (e.g. data from our study for maize fed D. magna); 2) for additional experiments the inclusion of multiple unrelated non-GE comparators should be considered; In addition, it should be taken into account that nutritional stress can affect the outcome of the study.

Subchronic toxicity study in rats evaluating herbicide-tolerant soybean DAS-68416-4.

A subchronic toxicity study was conducted in Wistar rats to evaluate the potential health effects of genetically modified (GM) herbicide-tolerant soybean DAS-68416-4. Rats were fed with diets containing toasted meal produced from GM soybean engineered with aad-12 and pat genes or containing non-GM soybean at a dose of 30.0, 15.0, or 7.5%,w/w% and 0% (control group) for 90 consecutive days. Animals were evaluated for general behavior, body weight gain, food consumption, food use efficiency, etc. At the middle and end of the study, blood and serum samples were collected for routine and biochemical assays. Internal organs were taken for calculating relative weights and doing histopathological examination. The rats were active and healthy without any abnormal symptoms during the entire study period. No biological differences in hematological or biochemical indices were detected. No histopathological changes were observed. Under the conditions of this study, herbicide-tolerant soybean DAS-68416-4 did not cause any treatment-related effects in Wistar rats following 90 days of dietary administration.

DP-2Ø2216-6 maize does not adversely affect rats in a 90-day feeding study.

Maize plants containing event DP-2Ø2216-6 (DP202216), which confers herbicide tolerance through expression of phosphinothricin acetyltransferase and enhanced grain yield potential via temporal modulation of the native ZMM28 protein, were developed for commercialization. To address current regulatory expectations, a mandatory 90-day rodent feeding study was conducted to support the safety assessment. Diets containing 50% by weight of ground maize grain from DP202216, non-transgenic control, and 3 non-transgenic reference varieties, were fully characterized, along with the grain, and diets were fed to Crl:CD®(SD) rats for at least 90 days. As anticipated, no biologically-relevant effects or toxicologically-significant differences were observed on survival, body weight/gain, food consumption/efficiency, clinical and neurobehavioral evaluations, ophthalmology, clinical pathology (hematology, coagulation, clinical chemistry, urinalysis), organ weights, or gross and microscopic pathology parameters in rats fed a diet containing up to 50% DP202216 maize grain when compared with rats fed diets containing control or reference maize grains. The results of this study support the conclusion that maize grain from plants containing event DP-2Ø2216-6 is as safe and nutritious as maize grain not containing the event and add to the significant existing database of rodent subchronic studies demonstrating the absence of hazards from consumption of edible fractions of genetically modified plants.

Bt Proteins Exacerbate Negative Growth Effects in Juvenile Rusty (F. rusticus) Crayfish Fed Corn Diet.

The adoption of genetically modified (GM) crops has occurred rapidly in the United States. The transfer of GM corn byproducts from agricultural fields to nearby streams after harvest is significant and occurs well into the post-harvest year. These corn leaves, stems, and cobs then become a detrital food source for organisms, such as shredders in the stream ecosystem. Considering that the nontarget effects of Bt corn have been observed in some terrestrial organisms, we assessed whether Bt toxins affect an important aquatic organism, juvenile F. rusticus crayfish. Juvenile crayfish were fed six distinct diet treatments: two varieties of Bt corn, two non-Bt controls of herbicide tolerant corn, and two controls: fish gelatin and river detritus. Juveniles were fed these diets while housed in flow-through artificial streams that received natural stream water from a local source. Specific growth rate and survivorship of the crayfish were measured throughout the study. Juveniles fed corn diets grew significantly less and had reduced survival compared with juveniles fed fish gelatin or river detritus diets. Furthermore, juveniles fed one Bt variety of corn (VT Triple Pro®) exhibited significantly less growth than those fed one of the herbicide tolerant varieties (Roundup Ready 2®). Our study shows that corn inputs to streams may be detrimental to the growth and survivorship of juvenile crayfish and that certain Bt varieties may exacerbate these negative effects. These effects on crayfish will have repercussions for the entire ecosystem, because crayfish are conduits of energy between many trophic levels.

Bacillus thuringiensis Maize Expressing a Fusion Gene Cry1Ab/Cry1AcZM Does Not Harm Valued Pollen Feeders.

The ladybird Propylea japonica, adults of the green lacewing Chrysoperla nipponensis and the honey bee Apis mellifera are common pollen feeders in many crop systems. They could therefore be directly exposed to Cry proteins in Bacillus thuringiensis (Bt)-transgenic crop fields by ingestion of pollen. They, or closely related species, are therefore often selected as surrogate test species in non-target risk assessment of Bt plants. In the current study, we evaluated the potential effects of the ingestion of Bt maize pollen containing the Cry1Ab/Cry1Ac fusion protein on various life-table parameters of the three pollen-feeding non-target species in laboratory feeding assays. The results showed that pupation rate and male adult fresh weight of P. japonica were significantly increased when fed pollen from Bt maize compared to control maize pollen, but other test life-table parameters were not affected. For the other two species, none of the tested life-table parameters (survival, pre-oviposition period, fecundity and adult fresh weight for C. nipponensis; survival and mean acinus diameter of hypopharyngeal glands for A. mellifera) differed between non-Bt and Bt maize pollen treatments. ELISA measurements confirmed the stability and uptake of the Cry protein by all three species during the feeding bioassays. In addition, a sensitive insect bioassay confirmed the bioactivity of the Cry1Ab/Cry1Ac protein in the Bt maize pollen used. Overall, the results suggested that the three pollen feeders are not sensitive to the Cry1Ab/Cry1Ac protein, and planting of the Bt maize variety will pose a negligible risk to P. japonica, adult C. nipponensis and adult A. mellifera.

The food safety of DP-356Ø43 soybeans on SD rats reflected by physiological variables and fecal microbiota during a 90-day feeding study.

Soybean is an important food resource for the eastern countries and herbicide-tolerant genetically modified soybeans (GMS) were widely developed to deal with weeds problems. Unprocessed soybean flour instead of dehulled and defatted soybean meal was used to reflect the safety of soybean food in whole. Rats were given formulated diets containing DP-356Ø43 or non-GM soybean JACK at an incorporation rate of 7.5%, 15%, or 30% (w/w), respectively for 90 days. Targeted traditional toxicological response variables were measured to reflect the holistic health of animals. No treatment-related adverse or toxic effects were observed based on an examination of the daily clinical signs, body weight, food consumption, hematology, serum biochemistry, and organ weight or based on gross and histopathological examination. The results demonstrate that the soybean DP-356Ø43 is as safe for consumption as conventional soybean JACK. In the current study, the effect of a herbicide-tolerant GMS DP-356043 on identified intestinal microbiota was evaluated in a rodent feeding study compared with its conventional control JACK. Feces samples from rats consuming different diets were collected before the start of the experiment (time 0) and at monthly intervals (at the end of the 1st, 2nd and 3rd months) over the course of 90 days. Six types of bacterias shared by humans and rats were detected with Q-PCR. The results of QPCR indicated that the GMS 356Ø43 had a comparable effect on the abundance of Bifidobacterium group, Clostridium perfringens subgroup, Escherichia coli, and Bacteroides-Prevotella group as the non-GMS JACK.

Humoral and cellular immune response in Wistar Han RCC rats fed two genetically modified maize MON810 varieties for 90 days (EU 7th Framework Programme project GRACE).

The genetically modified maize event MON810 expresses a Bacillus thuringiensis-derived gene, which encodes the insecticidal protein Cry1Ab to control some lepidopteran insect pests such as the European corn borer. It has been claimed that the immune system may be affected following the oral/intragastric administration of the MON810 maize in various different animal species. In the frame of the EU-funded project GRACE, two 90-day feeding trials, the so-called studies D and E, were performed to analyze the humoral and cellular immune responses of male and female Wistar Han RCC rats fed the MON810 maize. A MON810 maize variety of Monsanto was used in the study D and a MON810 maize variety of Pioneer Hi-Bred was used in the study E. The total as well as the maize protein- and Cry1Ab-serum-specific IgG, IgM, IgA and IgE levels, the proliferative activity of the lymphocytes, the phagocytic activity of the granulocytes and monocytes, the respiratory burst of the phagocytes, a phenotypic analysis of spleen, thymus and lymph node cells as well as the in vitro production of cytokines by spleen cells were analyzed. No specific Cry1Ab immune response was observed in MON810 rats, and anti-maize protein antibody responses were similar in MON810 and control rats. Single parameters were sporadically altered in rats fed the MON810 maize when compared to control rats, but these alterations are considered to be of no immunotoxicological significance.

Subchronic toxicity study in rats evaluating genetically modified DAS-81419-2 soybean.

A 90-day feeding study in rats was conducted to evaluate the subchronic oral toxicity of genetically modified (GM) DAS-81419-2 soybean. Wistar rats were fed with diets containing toasted soybean meal produced from DAS-81419-2 soybean grain that expresses the Cry1F, Cry1Ac, and Pat proteins or containing conventional soybean at doses of 30.0%, 15.0%, 7.5%, or 0% (control group) for 90 consecutive days. The general behavior, body weight and food consumption were observed. At the middle and end of the experiment, blood, serum, and urine samples were collected for biochemical assays. At the conclusion of the study, the internal organs were weighed and histopathological examination was completed. The rats exhibited free movement and shiny coats without any abnormal symptoms or abnormal secretions in their noses, eyes, or mouths. There were no adverse effects on body weight in GM soybean groups and conventional soybean groups. No biological differences in hematological, biochemical, or urine indices were observed. No significant differences in relative organ weights were detected between the experimental groups and the control group. No histopathological changes were observed. Under the conditions of this study, DAS-81419-2 soybean did not cause any treatment-related effects in Wistar rats following 90 days of dietary administration.

Bt Proteins Have No Detrimental Effects on Larvae of the Green Lacewing, Chrysopa pallens (Rambur) (Neuroptera: Chrysopidae).

Biosafety of a genetically modified crop is required to be assessed prior to its commercialization. For this, a suitable artificial diet was developed and used to establish a dietary exposure test for assessing the toxicity of midgut-active Bt insecticidal proteins on Chrysopa pallens (Rambur). Subsequently, this dietary exposure test was used to evaluate the toxicity of the proteins Cry1Ab, Cry1Ac, Cry1Ah, Cry1Ca, Cry1F, Cry2Aa, Cry2Ab, and Vip3Aa on C. pallens larvae. Temporal stability, bioactivity, and the intake of the insecticidal proteins were confirmed by enzyme-linked immunosorbent assay and a sensitive-insect bioassay. The life history characteristics, such as survival, pupation, adult emergence, 7-day larval weight, larval developmental time, and emerged male and female fresh weights remained unaffected, when C. pallens were fed the pure artificial diet (negative control) and the artificial diets containing 200 µg/g of each purified protein: Cry1Ab, Cry1Ac, Cry1Ah, Cry1Ca, Cry1F, Cry2Aa, Cry2Ab, or Vip3Aa. On the contrary, all of the life history characteristics of C. pallens larvae were adversely affected when fed artificial diet containing boric acid (positive control). The results demonstrate that diets containing the tested concentrations of Cry1Ab, Cry1Ac, Cry1Ah, Cry1Ca, Cry1F, Cry2Aa, Cry2Ab, and Vip3Aa have null effects on C. pallens larvae. The outcome indicates that genetically modified crops expressing the tested Bt proteins are safe for the lacewing, C. pallens.

Biotoxicity of Cry1Ab protein on wolf spider Pardosa pseudoannulata.

In this research, we carried out a tritrophic bioassay to assess the potential effect of Cry1Ab-expressing rice on the foraging behavior of the common wolf spider Pardosa pseudoannulata and its underlying molecular mechanism. Results indicated the Bt-containing spiders expressed a higher foraging range when compared to controls. The high throughput de novo transcriptome sequencing was further carried out for central nervous system (CNS) of P. pseudoannulata with and without Cry1Ab intake. We obtained 120, 985 unigenes with a mean length of 529.73 bp. Functional analysis of differentially expressed genes (DEGs) showed the expression levels of genes related to energy metabolism were changed in response to Cry1Ab, which may contribute to a more active foraging behavior. In addition, some DEGs also have a function related to metal ion binding, implying a potential influence on metal ions-dependent reactions. This may be associated with Cry1Ab resistance mechanism in the spider.

Procedure to select test organisms for environmental risk assessment of genetically modified crops in aquatic systems.

For a long time, the environmental risk assessment (ERA) of genetically modified (GM) crops focused mainly on terrestrial ecosystems. This changed when it was scientifically established that aquatic ecosystems are exposed to GM crop residues that may negatively affect aquatic species. To assist the risk assessment process, we present a tool to identify ecologically relevant species usable in tiered testing prior to authorization or for biological monitoring in the field. The tool is derived from a selection procedure for terrestrial ecosystems with substantial but necessary changes to adequately consider the differences in the type of ecosystems. By using available information from the Water Framework Directive (2000/60/EC), the procedure can draw upon existing biological data on aquatic systems. The proposed procedure for aquatic ecosystems was tested for the first time during an expert workshop in 2013, using the cultivation of Bacillus thuringiensis (Bt) maize as the GM crop and 1 stream type as the receiving environment in the model system. During this workshop, species executing important ecological functions in aquatic environments were identified in a stepwise procedure according to predefined ecological criteria. By doing so, we demonstrated that the procedure is practicable with regard to its goal: From the initial long list of 141 potentially exposed aquatic species, 7 species and 1 genus were identified as the most suitable candidates for nontarget testing programs. Integr Environ Assess Manag 2017;13:974-979. © 2017 SETAC.

A 90-day toxicity study of GmTMT transgenic maize in Sprague-Dawley rats.

GmTMT transgenic maize is a genetically modified maize plant that overexpresses the γ-tocopherol methyltransferase (γ-TMT) from Glycine max (Gm). The γ-TMT gene was introduced into maize line Zhen58 to encode the GmTMT2a protein which can convert γ-tocopherol into α-tocopherol. Overexpression of GmTMT2a significantly increased the α-tocopherol content in transgenic maize. The present study was designed to investigate any potential effects of GmTMT maize grain in a 90-day subchronic rodent feeding study. Maize grains from GmTMT or Zhen58 were incorporated into rodent diets at low (12.5%), medium (25%) or high (50%) concentrations and administered to Sprague-Dawley rats (n = 10/sex/group) for 90 days. The negative control group of rats (n = 10/sex/group) were fed with common maize diets. Results from body weights, feed consumption, clinical chemistry, hematology, absolute and relative organ weights indicated no treatment-related side effects of GmTMT maize grain on rats in comparison with rats consuming diets containing Zhen58 maize grain. In addition, no treatment-related changes were found in necropsy and histopathology examinations. Altogether, our data indicates that GmTMT transgenic maize is as safe and nutritious as its conventional non-transgenic maize.

Three-generation reproduction toxicity study of genetically modified rice with insect resistant genes.

In the present work, we evaluated the three generation reproductive toxicity of the genetically modified rice with insectresistant cry1Ac and sck genes. 120 Sprague-Dawley (SD) rats were divided into three groups which were fed with genetically modified rice diet (GM group), parental control rice diet (PR group) and AIN-93 control diet (both used as negative control) respectively. Bodyweight, food consumption, reproductive data, hematological parameters, serum chemistry, relative organ weights and histopathology for each generation were examined respectively. All the hematology and serum chemistry parameters, organ/body weight indicators were within the normal range or no change to the adverse direction was observed, although several differences in hematology and serum chemistry parameters (WBC, BUN, LDH of male rat, PLT, PCT, MPV of female rats), reproductive data (rate of morphologically abnormal sperm) were observed between GM rice group and two control groups. No macroscopic or histological adverse effects were found or considered as treatment-related, either. Overall, the three generation study of genetically modified rice with cry1Ac and sck genes at a high level showed no unintended adverse effects on rats's reproductive system.

Variability of control data and relevance of observed group differences in five oral toxicity studies with genetically modified maize MON810 in rats.

The data of four 90-day feeding trials and a 1-year feeding trial with the genetically modified (GM) maize MON810 in Wistar Han RCC rats performed in the frame of EU-funded project GRACE were analysed. Firstly, the data obtained from the groups having been fed the non-GM maize diets were combined to establish a historical control data set for Wistar Han RCC rats at the animal housing facility (Slovak Medical University, Bratislava, Slovakia). The variability of all parameters is described, and the reference values and ranges have been derived. Secondly, the consistency of statistically significant differences found in the five studies was analysed. In order to do so, the body weight development, organ weight, haematology and clinical biochemistry data were compared between the studies. Based on the historical control data, equivalence ranges for these parameters were defined, and the values measured in the GM maize-fed groups were compared with these equivalence ranges. Thirdly, the (statistical) power of these feeding studies with whole food/feed was assessed and detectable toxicologically relevant group differences were derived. Linear mixed models (LMM) were applied, and standardized effect sizes (SES) were calculated in order to compare different parameters as well as to provide an overall picture of group and study differences at a glance. The comparison of the five feeding trials showed a clear study effect in the control data. It also showed inconsistency both in the frequency of statistically significant differences and in the difference values between control and test groups.

Effect of genetically modified corn on the jejunal mucosa of adult male albino rat.

Genetically modified (GM) plants expressing insecticidal traits offer a new strategy for crop protection. GM-corn contains Bacillus thuringiensis (Bt) genes producing delta endotoxins in the whole plant. Diet can influence the characteristics of the gastrointestinal tract altering its function and structure. The aim of this study was to evaluate the effect of GM-corn on the histological structure of jejunal mucosa of adult male albino rat using different histological, immunohistochemical and morphometrical methods. Twenty adult male albino rats were divided into two equal groups; control and GM-corn fed group administered with 30% GM-corn for 90days. Specimens from the jejunum were processed for light and electron microscopy. Immunohistochemical study was carried out using antibody against proliferating cell nuclear antigen (PCNA). Different morphometrical parameters were assessed. Specimens from GM-corn fed group showed different forms of structural changes. Focal destruction and loss of the villi leaving denuded mucosal surface alternating with stratified areas were observed, while some crypts appeared totally disrupted. Congested blood capillaries and focal infiltration with mononuclear cells were detected. Significant upregulation of PCNA expression, increase in number of goblet cells and a significant increase in both villous height and crypt depth were detected. Marked ultrastructural changes of some enterocytes with focal loss of the microvillous border were observed. Some enterocytes had vacuolated cytoplasm, swollen mitochondria with disrupted cristae and dilated rough endoplasmic reticulum (rER). Some cells had dark irregular nuclei with abnormally clumped chromatin. It could be concluded that consumption of GM-corn profoundly alters the jejunal histological structure.

Occupational hazards and health cost of women cotton pickers in Pakistani Punjab.

BACKGROUND: Farm workers and female cotton pickers are exposed to residual impacts of pesticide use in cotton production, in addition to dust, ultraviolet radiation, etc. Cotton picking causes various health hazards among cotton pickers with varied health cost. A soil bacterium known as Bacillus thuringiensis (Bt) is incorporated in cotton seed through genetic modification and it has resistance against certain bollworms of cotton. So it is considered that Bt cotton fields have less pesticide exposure compared to non-Bt cotton fields. This study was designed to examine and compare the impacts and health cost of cotton picking among female cotton pickers working in Bt and non-Bt cotton fields. METHODS: The study used the data collected from Vehari district of Pakistani Punjab. Health hazards and associated health cost of the respondents involved in Bt cotton picking were compared with those who harvested non-Bt cotton. Comparative use of the personal protective measures among those respondents was also examined. Health cost function and its determinants were analyzed using ordinary least square method. RESULTS: Findings of the study showed that 61 % cotton pickers from Bt cotton households reported one or more health effects of pesticide during picking season whereas this percentage for non-Bt cotton households was 66 %. Health impacts included skin problems, headache, cough, flu/fever, eye irritation and sleeplessness, however, percentage of these health impacts was comparatively higher among non-Bt cotton households. Health cost from exposure to pesticide use in cotton was US$ 5.74 and 2.91 per season for non-Bt cotton and Bt cotton households, respectively. Education, picking in Bt cotton fields and preventive measures were significantly related with health cost. CONCLUSION: Cotton pickers working in Bt cotton fields are found to have less occupational health hazards compared to those working in non-Bt cotton fields. Thus generating awareness among cotton pickers for adopting precautionary measures during harvesting and the use of Bt cotton seed can result in a decline in the ill-effects of cotton picking.