Weight of the evidence on the human carcinogenicity of 2,4-D

Exposure of the African mound building termite, Macrotermes bellicosus workers to commercially formulated 2,4-D and atrazine caused high mortality and impaired locomotor response

Recent empirical evidence suggests that herbicides have damaging effects on non-target organisms in both natural and semi-natural ecosystems. The African mound building termite, Macrotermes bellicosus, is an important beneficial insect that functions as an ecosystem engineer due to its role in the breakdown of dead and decaying materials. Here, we examined the effects of 2,4-D amine salt (2,4-D) and atrazine based herbicides viz. Vestamine® and Ultrazine® on the survival and locomotion response of M. bellicosus. Worker termites were treated with a range of concentrations of Vestamine® (the recommended concentration: 6.25 ml per 500 ml of water, 0.25- and 0.5-fold below the recommended concentration and distilled water as control) and Ultrazine® (the recommended concentration: 3.75 ml per 500 ml of water, 0.25-, 0.5-, 2.0- and 4-fold of the recommended concentration and distilled water as control) for 24 hours for the mortality test, and allowed to run for 15 seconds for the locomotion trial. All concentrations of both Vestamine® and Ultrazine® were highly toxic to worker termites and mortality increased as the concentration and time after treatment increased. For both herbicides, concentrations far less than the recommended rates caused 100% mortality. The speed of termites was significantly influenced by both Vestamine® and Ultrazine® as termites exposed to all tested concentrations of the herbicides exhibited reduced running speed than the control. These findings suggest that beneficial insects, especially M. bellicosus may experience high mortality (up to 100%) and reduced mobility if they are sprayed upon or come in contact with plant materials that have been freshly sprayed with (less or more than) the recommended concentrations of Vestamine® and Ultrazine®. The findings of our study calls for the reassessment of the usage of 2,4-D and atrazine based herbicides in weed control in termite and other beneficial insect populated habitats.

Determination of 2,4-Dichlorophenoxyacetic acid (2,4-D) in rat serum for pharmacokinetic studies with a simple HPLC method

2,4-Dichlorophenoxyacetic acid (2,4-D) is a chlorophenoxy herbicide used worldwide. We describe a high-performance liquid chromatography (HPLC) method with UV detection for the determination of 2,4-D in female and male rat serum. This allows to observe the change of serum 2,4-D concentration in rats with time and its pharmacokinetics characteristics with a simple, rapid, optimized and validated method. The serum samples are pretreated and introduced into the HPLC system. The analytes are separated in a XDB-C18 column with a mobile phase of acetonitrile (solvent A) and 0.02 M ammonium acetate (containing 0.1% formic acid) (solvent B) using a gradient elution at a flow rate of 1.0 mL/min. The wavelength for UV detection was set at 230 nm. Calibration curve for 2,4-D was constructed over a range of 0.1-400 mg/L. The method was successfully applied to study the pharmacokinetics of 2,4-D in rats in this study. After oral administration of 300 mg/kg and 60 mg/kg 2,4-D, the mean Cmax values were 601.9 and 218.4 mg/L, the AUC0→∞ values were 23,722 and 4,127 mg×h/L and the clearance (Cl) were 1.10 and 0.02 L/(h×kg), respectively. The developed method was found to be specific, precise, reproducible and rapid.

Highly Sensitive, Label-Free Detection of 2,4-Dichlorophenoxyacetic Acid Using an Optofluidic Chip

A highly sensitive approach for rapid and label-free detection of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) using an optofluidic chip is demonstrated. The optofluidic chip is prepared by covalent immobilization of 2,4-D-bovine serum albumin (2,4-D-BSA) conjugate to an integrated microring resonator. Subsequent detection of 2,4-D carried out in a competitive immunoreaction format enables selective detection of 2,4-D in different types of water samples, including bottled, tap, and lake water, at a limit of detection (LOD) of 4.5 pg/mL and in a quantitative range of 15-10⁵ pg/mL. The microring resonator-based optofluidic chip is reusable with ultrahigh sensitivity that offers real-time and on-site detection of low-molecular-weight targets for potential applications in food safety and environmental monitoring.

A Comprehensive, Integrated Review and Evaluation of the Scientific Evidence Relating to the Safety of the Herbicide 2,4-D

The safety of 2,4-D to farm and forestry workers, commercial applicators and the general public has been of continuing concern because certain epidemiological studies of groups potentially exposed to 2,4-D have suggested a relationship between 2,4-D use and increased risk of soft tissue sarcoma, Hodgkin's disease or non-Hodgkin's lymphoma. This review on 2,4-D is unique in that the approach taken was to integrate data from worker exposure studies, whole animals, metabolic and other relevant laboratory studies with the epidemiological findings to assess the extent to which there is scientific support for the hypothesis that 2,4-D exposure is associated with any increased risk of human cancer.

The case-control epidemiological studies that have been the source of the cancer risk hypothesis are inconclusive. Problems in assessing exposure based on patients' memories make these studies difficult to interpret. Cohort studies of exposed workers do not generally support the specific hypothesis that 2,4-D causes cancer. Taken together, the epidemiological studies provide, at best, only weak evidence of an association between 2,4-D and the risk of cancer.

Importantly, the cancer hypothesis is not supported by other data. A critical evaluation of the exposure data indicates that exposure to 2,4-D in user groups is intermittent and much lower than the doses tested chronically in long-term animal studies that have not shown evidence of tumor induction. Moreover, the structure of 2,4-D does not suggest it would be a carcinogen. 2,4-D is a simple organic acid, that is largely excreted unchanged, and there is no evidence that it is metabolized to critically reactive metabolites or accumulates in tissues. This evidence is supported by a large body of negative studies on genotoxicity, which taken together with the metabolic studies, clearly indicates that 2,4-D is highly unlikely to be a genotoxic carcinogen. Furthermore, 2,4-D has no known hormonal activity and does not induce proliferative changes in any tissue or organ, indicating that it does not possess any of the characteristics of non-genotoxic animal carcinogens. Thus the available mechanistic studies provide no plausible basis for a hypothesis of carcinogenicity.

In this review, data relating to potential neurotoxicity, immunotoxicity and reproductive toxicity also were evaluated. There is no evidence that 2,4-D adversely affects the immune system and neurotoxic and reproductive effects only have been associated with high toxic doses that would not be encountered by 2,4-D users.

Historical exposures to 2,4-D by user groups, particularly farmers, forestry workers and commercial applicators, would be higher than those sustained under present rigorous standards for application which involve the use of protective clothing and other measures to reduce exposure. Proposed label changes indicate that in the future exposures will be even further reduced. Viewed in this context, the available data indicate that the potential public health impact of 2,4-D, including the risk of human cancer, was negligible in the past and would be expected to be even smaller in the present and future.

Phenoxy herbicides, soft-tissue sarcoma and non-Hodgkin lymphoma: a systematic review of evidence from cohort and case-control studies

BACKGROUND

Phenoxy herbicides have been used widely in agriculture, forestry, parks and domestic gardens. Early studies linked them with soft-tissue sarcoma (STS) and non-Hodgkin lymphoma (NHL), but when last reviewed by the International Agency for Research on Cancer in 1986, the evidence for human carcinogenicity was limited.

SOURCES OF DATA

We searched Medline and Embase, looking for cohort or case-control studies that provided data on risk of STS and/or NHL in relation to phenoxy herbicides, and checked the reference lists of relevant publications for papers that had been missed.

AREAS OF AGREEMENT, AREAS OF CONTROVERSY

The extensive evidence is not entirely consistent, and a hazard of STS or NHL cannot firmly be ruled out. However, if there is a hazard, then absolute risks must be small.

GROWING POINTS, AREAS TIMELY FOR DEVELOPING RESEARCH

Extended follow-up of previously assembled cohorts may be the most efficient way of further reducing uncertainties.

Soft tissue sarcoma, non-Hodgkin's lymphoma and chronic lymphocytic leukaemia in workers exposed to phenoxy herbicides: extended follow-up of a UK cohort

OBJECTIVES

To provide further information on the possible carcinogenicity of phenoxy herbicides, and in particular their relationship to soft tissue sarcoma (STS), non-Hodgkin's lymphoma (NHL) and chronic lymphocytic leukaemia (CLL).

METHODS

We extended follow-up to December 2012 for 8036 men employed at five factories in the UK which had manufactured phenoxy herbicides, or in a contract spraying business. Mortality was compared with that for England and Wales by the person-years method. Nested case-control analyses compared men with incident or fatal STS (n=15) or NHL/CLL (n=74) and matched controls (up to 10 per case).

RESULTS

4093 men had died, including 2303 since the last follow-up. Mortality from all causes and all cancers was close to expectation, but an excess of deaths from NHL was observed among men who had worked for ≥1 year in jobs with more than background exposure to phenoxy herbicides (19 deaths, SMR 1.85, 95% CI 1.12 to 2.89). Four deaths from STS occurred among men potentially exposed above background (3.3 expected). In the nested case-control analyses, there were no significantly elevated risks or consistent trends across categories of potential exposure for either STS or NHL/CLL. Among men who had worked for ≥1 year in potentially exposed jobs, the highest OR (for STS) was only 1.30 (95% CI 0.30 to 5.62).

CONCLUSIONS

Our findings are consistent with the current balance of epidemiological evidence. If phenoxy herbicides pose a hazard of either STS or NHL, then any absolute increase in risk is likely to be small.

Can mitochondrial dysfunction be initiated by dissociative electron attachment to xenobiotics?

Resonance attachment of low-energy electrons to xenobiotic molecules, 2,4-dichlorophenoxyacetic acid (2,4-D), dichlorodiphenyltrichloroethane (DDT) and dichlorodiphenyldichloroethylene (DDE), was investigated under gas-phase conditions by means of complementary experimental techniques. Electron transmission spectroscopy (ETS) and dissociative electron attachment spectroscopy (DEAS), in the 0-6 eV and 0-15 eV energy range, respectively, were applied with the aim of modeling the behavior of these pesticide molecules under reductive conditions in vivo. Formation of long-lived parent molecular anions and fragment negative ions was observed at incident electron energies very close to zero, in agreement with the results of density functional theory calculations. The gas-phase DEA process, analogous to dissociative electron transfer in solution, was considered as a model for the initial step which occurs in the intermembrane space of mitochondria when a xenobiotic molecule captures an electron "leaked" from the respiratory chain. A possible involvement of the fragments produced by DEA to the pesticides under investigation into cellular processes is discussed. It is concluded that the free radicals and potential DNA adducts formed by DEA are expected to be dangerous for mitochondrial functionalities, while several of the products observed could act as messenger molecules, thus interfering with the normal cellular signaling pathways.

A Systematic Review of Carcinogenic Outcomes and Potential Mechanisms from Exposure to 2,4-D and MCPA in the Environment

Chlorophenoxy compounds, particularly 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-chloro-2-methylphenoxy)acetic acid (MCPA), are amongst the most widely used herbicides in the United States for both agricultural and residential applications. Epidemiologic studies suggest that exposure to 2,4-D and MCPA may be associated with increased risk non-Hodgkins lymphoma (NHL), Hodgkin's disease (HD), leukemia, and soft-tissue sarcoma (STS). Toxicological studies in rodents show no evidence of carcinogenicity, and regulatory agencies worldwide consider chlorophenoxies as not likely to be carcinogenic or unclassifiable as to carcinogenicity. This systematic review assembles the available data to evaluate epidemiologic, toxicological, pharmacokinetic, exposure, and biomonitoring studies with respect to key cellular events noted in disease etiology and how those relate to hypothesized modes of action for these constituents to determine the plausibility of an association between exposure to environmentally relevant concentrations of 2,4-D and MCPA and lymphohematopoietic cancers. The combined evidence does not support a genotoxic mode of action. Although plausible hypotheses for other carcinogenic modes of action exist, a comparison of biomonitoring data to oral equivalent doses calculated from bioassay data shows that environmental exposures are not sufficient to support a causal relationship. Genetic polymorphisms exist that are known to increase the risk of developing NHL. The potential interaction between these polymorphisms and exposures to chlorophenoxy compounds, particularly in occupational settings, is largely unknown.

Yeast toxicogenomics: genome-wide responses to chemical stresses with impact in environmental health, pharmacology, and biotechnology

The emerging transdisciplinary field of Toxicogenomics aims to study the cell response to a given toxicant at the genome, transcriptome, proteome, and metabolome levels. This approach is expected to provide earlier and more sensitive biomarkers of toxicological responses and help in the delineation of regulatory risk assessment. The use of model organisms to gather such genomic information, through the exploitation of Omics and Bioinformatics approaches and tools, together with more focused molecular and cellular biology studies are rapidly increasing our understanding and providing an integrative view on how cells interact with their environment. The use of the model eukaryote Saccharomyces cerevisiae in the field of Toxicogenomics is discussed in this review. Despite the limitations intrinsic to the use of such a simple single cell experimental model, S. cerevisiae appears to be very useful as a first screening tool, limiting the use of animal models. Moreover, it is also one of the most interesting systems to obtain a truly global understanding of the toxicological response and resistance mechanisms, being in the frontline of systems biology research and developments. The impact of the knowledge gathered in the yeast model, through the use of Toxicogenomics approaches, is highlighted here by its use in prediction of toxicological outcomes of exposure to pesticides and pharmaceutical drugs, but also by its impact in biotechnology, namely in the development of more robust crops and in the improvement of yeast strains as cell factories.

Prediction of pesticides chromatographic lipophilicity from the computational molecular descriptors

Quantitative structure-property relationship models were developed for the prediction of pesticides and some PAH compounds lipophilicity based on a wide set of computational molecular descriptors and a set of experimental chromatographic data. The chromatographic lipophilicity of pesticides has been evaluated by high-performance liquid chromatography (HPLC) using different chemically bonded (C18, C8, CN and Phenyl HPLC columns) stationary phases and two different organic modifiers (methanol and acetonitrile, respectively) in the mobile phase composition. Through a systematic study, by using the classic multivariate analysis, several quantitative structure-property/lipophilicity multi-dimensional models were established. Multiple linear regression and genetic algorithm for the variable subset selection were used. The internal and external statistical evaluation procedures revealed some appropriate models for the chromatographic lipophilicity prediction of pesticides. Moreover, the statistical parameters of regression and those obtained by applying t-test for the intercept (a(0)) and for the slope (a(1)) in order to evaluate relationship between experimental and predicted octanol-water partition coefficients in case of the test set compounds, revealed two statistically valid models that can be successfully used in lipophilicity prediction of pesticides.

Purification of seawater contaminated with undegradable aromatic ring compounds using ozonolysis followed by titanium dioxide treatment

Treatment of aromatic ring compounds, 2,4-dichlorophenoxy acetic acid (2,4-D), 2,4,5-trichloro-phenoxy acetic acid (2,4,5-T), and bisphenol A, in the artificial seawater, i.e. Allen seawater, was carried out by ozonation and titanium dioxide (TiO2) photocatalyst treatment. Each compound was degraded and varnished within 30 min by only ozonolysis at pH 9.0 and at 20 degrees C, while the TOC value of each compound decreased gradually but reached almost constant value, i.e. about 70-80% of the initial value, at even 30 min of ozonation time. Ozonolysis (30 min of ozonation time) followed by TiO2 photocatalyst treatment (50h of reaction time) was a very effective method for decreasing the TOC values of aromatic ring compounds in the artificial seawater. In consequence, TOC values of 2,4-D, 2,4,5-T, and bisphenol A could be reduced to about 28, 21, and 34% of their initial values, respectively.

Review and Meta-analysis of Risk Estimates for Prostate Cancer in Pesticide Manufacturing Workers

PURPOSE

The purpose of the present paper is to review cohort studies that examined the occurrence of prostate cancer in pesticide manufacturing workers in order to undertake a qualitative and quantitative evaluation of the risk as well as to assess the level of epidemiological evidence for each class of chemical compounds.

METHODS

Following a systematic literature search, relative risk (RR) estimates for prostate cancer were extracted from 18 studies published between 1984 and 2004. All studies were summarised and evaluated for homogeneity and publication bias. As no significant heterogeneity was detected, combined RR estimators were calculated using a fixed effect model. Meta-analyses were performed both on the whole set of data and for each chemical class separately.

RESULTS

The meta-rate ratio estimate for all studies was 1.28 [95% confidence interval (CI) 1.05-1.58]. After stratification by specific chemical class, consistent increases in the risk of prostate cancer were found in all groups but statistical significance was found only for accidental or non-accidental exposure to phenoxy herbicides contaminated with dioxins and furans. There was no obvious indication of publication bias.

CONCLUSION

The overall meta-analysis provides additional quantitative evidence consistent with prior reviews focusing on other groups exposed to pesticides (farmers, pesticide applicators). The results again point to occupational exposure to pesticides as a possible risk factor for prostate cancer but the question of causality remains unanswered. Epidemiological evidence did not allow identifying a specific pesticide or chemical class that would be responsible for the increased risk but the strongest evidence comes from workers exposed to phenoxy herbicides possibly in relation with dioxin and/or furan contamination.

Early transcriptional response of Saccharomyces cerevisiae to stress imposed by the herbicide 2,4-dichlorophenoxyacetic acid

The global gene transcription pattern of the eukaryotic experimental model Saccharomyces cerevisiae in response to sudden aggression with the widely used herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) was analysed. Under acute stress, 14% of the yeast transcripts suffered a greater than twofold change. The yeastract database was used to predict the transcription factors mediating the response registered in this microarray analysis. Most of the up-regulated genes in response to 2,4-D are known targets of Msn2p, Msn4p, Yap1p, Pdr1p, Pdr3p, Stp1p, Stp2p and Rpn4p. The major regulator of ribosomal protein genes, Sfp1p, is known to control 60% of the down-regulated genes, in particular many involved in the transcriptional and translational machinery and in cell division. The yeast response to the herbicide includes the increased expression of genes involved in the oxidative stress response, the recovery or degradation of damaged proteins, cell wall remodelling and multiple drug resistance. Although the protective role of TPO1 and PDR5 genes was confirmed, the majority of the responsive genes encoding multidrug resistance do not confer resistance to 2,4-D. The increased expression of genes involved in alternative carbon and nitrogen source metabolism, fatty acid beta-oxidation and autophagy was also registered, suggesting that acute herbicide stress leads to nutrient limitation.

The weight of scientific evidence in policy and law

The term "weight of evidence" (WOE) appears in regulatory rules and decisions. However, there has been little discussion about the meaning, variations of use, and epistemic significance of WOE for setting health and safety standards. This article gives an overview of the role of WOE in regulatory science, discusses alternative views about the methodology underlying the concept, and places WOE in the context of the Supreme Court's decision in Daubert v Merrell Dow Pharmaceuticals, Inc (1993). I argue that whereas the WOE approach to evaluating scientific evidence is gaining favor among regulators, its applications in judicial processes may be in conflict with some interpretations of how the Daubert criteria for judging reliable evidence should be applied.

The herbicide 2,4-dichlorophenoxyacetic acid induces the generation of free-radicals and associated oxidative stress responses in yeast

The pro-oxidant action of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) is demonstrated in this study using Saccharomyces cerevisiae as a eukaryotic experimental model. Evidence is presented for the generation of hydroxyl-radicals, in yeast cells suddenly exposed to 2,4-D, detected by in vivo electron paramagnetic resonance (EPR) spectroscopy using 5,5'-dimethyl-1-pyrroline N-oxide and 5-tert-butoxycarbonyl-5-methyl-1-pyrroline N-oxide as spin-traps. The intensity of the EPR spectra was dependent on the concentration of herbicide tested and was consistently higher in a mutant (Deltasod1) devoid of the cytosolic CuZn-superoxide dismutase. A time-course-dependent variation of the level of free-radical adducts was registered upon sudden exposure of an yeast cell population to concentrations of 2,4-D that lead to an initial period of viability loss, before resumption of inhibited growth by the viable adapted population. The variation pattern of the level of hydroxyl-radical adducts correlated with the one determined for the activity of Sod1p, cytosolic catalase Ctt1p, and the dithiol glutaredoxins Grx1p and Grx2p.

Genotoxicity of 2,4-D and dicamba revealed by transgenic Arabidopsis thaliana plants harboring recombination and point mutation markers

The phenoxy herbicides 2,4-D and dicamba are released daily into the environment in large amount. The mechanisms of genotoxicity and mutagenicity of these herbicides are poorly understood, and the available genotoxicity data is controversial. There is a cogent need for a novel genotoxicity monitoring system that could provide both reliable information at the molecular level, and complement existing systems.We employed the transgenic Arabidopsis thaliana 'point mutation' and 'recombination' plants to monitor the genetic effects of the herbicides 2,4-D and dicamba. We found that both herbicides had a significant effect on the frequency of homologous recombination A-->G mutation. Neither herbicides affected the T-->G mutation frequency. Interestingly, these transgenic biomonitoring plants were able to detect the presence of phenoxy herbicides at concentrations that were lower than the guideline levels for Drinking Water Quality. The results of our studies suggest that our transgenic system may be ideal for the evaluation of the genotoxicity of herbicide-contaminated water. Moreover, the unique ability of the plants to detect both double-strand breaks (homologous recombination) and point mutations provides tremendous potential in the study of molecular mechanisms of genotoxicity and mutagenicity of phenoxy herbicides.

Quantitation of aberrant interlocus T-cell receptor rearrangements in mouse thymocytes and the effect of the herbicide 2,4-dichlorophenoxyacetic acid

Small studies in human populations have suggested a correlation between the frequency of errors in antigen receptor gene assembly and lymphoid malignancy risk. In particular, agricultural workers exposed to pesticides have both an increased risk for lymphoma and an increased frequency of errors in antigen receptor gene assembly. In order to further investigate the potential of such errors to serve as a mechanistically based biomarker of lymphoid cancer risk, we have developed a sensitive PCR assay for quantifying errors of V(D)J recombination in the thymocytes of mice. This assay measures interlocus rearrangements between two T-cell receptor loci, V-gamma and J-beta, located on chromosomes 13 and 6, respectively. The baseline frequency in four strains of mice was determined at several ages (2-8 weeks of age) and was found to be stable at approximately 1.5 x 10(-5) per thymocyte. Strain AKR, which has a high susceptibility to T-cell lymphomas, did not show an elevated frequency of aberrant V(D)J events. We used this assay to examine the effects of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) on the frequency of these events. Female B6C3F1 mice, 27 days of age, were exposed to 2,4-D by gavage at doses of 0, 3, 10, 30, and 100 mg/kg/day for 4 successive days and sacrificed on day 5. Thymus DNA was isolated and examined for illegitimate V(D)J recombination-mediated gene rearrangements. In addition, pregnant mice were exposed to 2,4-D and thymocytes from the offspring examined at 2 weeks of age. No significant increase in aberrant V(D)J rearrangements was found, indicating that under these conditions 2,4-D does not appear to effect this important mechanism of carcinogenesis.

Micronucleus frequency and proliferation in human lymphocytes after exposure to herbicide 2,4-dichlorophenoxyacetic acid in vitro and in vivo

Widespread use of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) and its association with non-Hodgkin's lymphoma (NHL) and other cancers has raised public concern. Here, micronucleus (MN) formation has been used as a biomarker of genotoxicity, and replicative and mitotic indices (MIs) as biomarkers of cell cycle kinetics in human lymphocytes. Cells were cultured either as whole blood or isolated lymphocytes and treated with pure or commercial forms of 2,4-D at doses between 0.001 and 1 mM for 48 h. Exposure to 2,4-D produced a minimal increase in MN in whole blood and even smaller one in isolated lymphocyte cultures. This induction took place only at levels approaching cytotoxicity and was accompanied by a significant inhibition of replicative index (RI). At a low (0.005 mM) dose of commercial 2,4-D, a small, marginally significant increase in RI (12-15%) was found in two independent sets of experiments (P=0.052). Additionally, we found that lymphocyte RI was more affected by commercial 2,4-D containing 9.4% of the chemically pure 2,4-D, than with an equal concentration of the latter suggesting that other ingredients present in the commercial pesticide may be responsible or may enhance the effect of 2,4-D. Mitotic index, however, did not show any significant change with either commercial or pure 2,4-D. The lymphocytes of 12 male applicators exposed solely to 2,4-D during a 3-month period had a significantly higher RI than the same group prior to exposure and than a control group (P<0.01), in accordance with the in vitro finding of increased RI at low doses.

Reversible surface thiol immobilization of carboxyl group containing haptens to a BIAcore biosensor chip enabling repeated usage of a single sensor surface

We describe a reversible immobilization method for carboxyl group containing haptens that makes the repeated usage of a BIAcore biosensor chip possible. Haptens which are immobilized according to the surface thiol method can be removed completely from the sensor surface again by a reducing step. In the first part of our study, analogues of the herbicides 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid were immobilized in succession to a biosensor surface of a BIAcore surface plasmon resonance instrument according to the thiol coupling method. Direct kinetic analysis of these ligands to a polyclonal anti-2,4-dichlorophenoxyacetic acid antibody were performed using these biosensor surfaces. In the second part of the study, different amounts of 2,4-dichlorophenoxyacetic acid were sequentially immobilized onto the same biosensor surface in order to generate a calibration plot for 2,4-dichlorophenoxyacetic acid. Using this plot, the quantitative detection of the herbicide down to a concentration of 0.1 microg/mL, the maximum admissible concentration of pesticides in drinking water, is possible.

Development of models to predict dose of pesticides in professional turf applicators

Epidemiologic studies designed to assess the chronic effects of pesticides are limited by inadequate measurements of exposures. Although cohort studies have been initiated to evaluate the effects of 2,4-dichlorophenoxyacetic acid (2,4-D) and other pesticides in professional turf applicators, they may have limited power to detect significant health risks and may be subject to bias from exposure measurement error. In this study, the doses of 2,4-D, mecoprop [2-(4-chloro-2 methylphenoxy) propionic acid, MCPP] and dicamba (3,6-dichloro-o-anisic acid) were evaluated in a group of 98 professional turf applicators from 20 companies across southwestern Ontario. During a 1-week period (Saturday to Thursday), the volume of pesticide (active ingredient) applied was only weakly related to the total dose of 2,4-D absorbed (R(2)=0.21). Two additional factors explained a large proportion of variation in dose: the type of spray nozzle used and the use of gloves while spraying. Individuals who used a fan-type nozzle had significantly higher doses than those who used a gun-type nozzle. Glove use was associated with significantly lower doses. Job satisfaction and current smoking influenced the dose but were not highly predictive. In the final multiple regression models predicting total absorbed dose of 2,4-D and mecoprop, approximately 63-68% of the variation was explained. The future application of these models for epidemiologic research will depend on the availability of information and records from employers, the feasibility of contacting study subjects and cost.

The effect of exposure to a commercial 2,4-D formulation during gestation on the immune response in CD-1 mice

Pregnant CD-1 mice were administered a commercial 2,4-dichlorophenoxyacetic acid (2,4-D) formulation on days 6-16 days of gestation, in drinking water at concentrations ranging from 0 to 1.0% of the formulated product, equivalent to approximately 0-650 mg/kg per day expressed as the amine derivative. The effect of 2,4-D on immune function was evaluated in offspring 7 weeks after birth. The dams tolerated repeated 2,4-D exposure in drinking water without difficulty. The offspring exhibited decreased body weight with minor reductions in the kidney weights in the 0.1 and 1.0% 2,4-D treatment groups. A generalized suppression of lymphocyte stimulation by concanavalin A (Con A) was observed at high dose of commercial 2,4-D formulation (1.0%). Cytometric studies of the lymphocyte subpopulations demonstrated an increased relative count of B cells and reduced T cytotoxic or suppressor cells in the 1.0% formulation. The humoral immune response, antibody production against sheep red blood cells and peritoneal macrophage phagocytic function, were not altered by 2,4-D. Since the immune alterations in the offspring were observed many weeks after exposure, it appears as though 2,4-D exposure during gestation causes permanent changes in cell types associated with immune function. Since 2,4-D is not considered a persistent chemical, it is unlikely that 2,4-D residues are contributing significantly to the observed immune alterations. The immune alterations were observed only in the higher treatment groups. Therefore, the impact on human and animal health from an immune perspective, which would be encountered following normal application in the environment, would be minimal.

Genotoxicity studies on the phenoxyacetates 2,4-D and 4-CPA in the Drosophila wing spot test

The phenoxyacetates 2,4-D and 4-CPA were evaluated for genotoxicity using the Drosophila melanogaster wing spot test, which assesses for somatic mutation and recombination events. Third-instar larvae trans-heterozygous for two recessive mutations affecting the expression of wing trichomes, multiple wing hairs (mwh), and flare (flr) were treated by chronic feeding with different concentrations of the two chemicals. Feeding lasted until pupation of the surviving larvae and the genotoxic effects induced were evaluated in adults for the appearance of wing-blade cell clones with the mwh, flr, or mwh-flr phenotypes. Exposure to 2,4-D, at the highest concentration evaluated (10 mM), induced a weak but significant increase in the frequency of two of the categories of recorded spots: large single and total spots; in contrast, the 4-CPA treatments failed to induce any significant increase in the frequency of evaluated spots. When the heterozygous larvae for mwh and the multiple inverted TM3 balancer chromosome were treated with the chemicals, no increases were detected, either after the 2,4-D nor the 4-CPA treatments.

Mortality study of pesticide applicators and other employees of a lawn care service company

In response to reports linking non-Hodgkin's lymphoma (NHL) and the herbicide 2,4-dichlorophenoxyacetic acid, a retrospective cohort mortality study of 32,600 employees of a lawn care company was conducted. The cohort was generally young with short-duration employment and follow-up. In comparison to the US population, the cohort had significantly decreased mortality from all causes of death combined (307 deaths), arteriosclerotic heart disease, and accidents. There were 45 cancer deaths (59.6 expected, standardized mortality ratio [SMR] = 0.76, 95% confidence interval [CI] = 0.55, 1.01). Bladder cancer mortality was significantly increased, but two of the three observed deaths had no direct occupational contact with pesticides. There were four deaths due to NHL (SMR = 1.14, CI = 0.31, 2.91); three were male lawn applicators (SMR = 1.63, CI = 0.33, 4.77), with two of the applicators employed for three or more years (SMR = 7.11, CI = 1.78, 28.42). No other cause of death was significantly elevated among lawn applicators as a group or among those employed for three or more years. Although based on very small numbers and perhaps due to chance, the NHL excess is consistent with several earlier studies.

Human cytochrome P450 3A4 is involved in the biotransformation of the herbicide 2,4-dichlorophenoxyacetic acid

2,4-Dichlorophenoxyacetic acid (2,4-D) is one of the most frequently used herbicides and is an environmental pollutant. Evidence exists that 2,4-D exposure results in an increased risk for certain malignant disorders such as nasal carcinoma and soft tissue sarcoma in humans and animals. The involvement of cytochrome P450 3A4 (CYP3A4), the major form of monooxygenase enzyme in human liver, in the metabolism of 2,4-D was studied using microsomal fractions and whole cells of Saccharomyces cerevisiae expressing cytochrome P450 3A4. 2,4-Dichlorophenol (2,4-DCP) was identified as the only product of metabolism by TLC followed by NMR and IR spectroscopy and a turnover of 0.13 nmol 2,4-DCP/min/nmol P450 was observed.

Brain tumor and exposure to pesticides in humans: a review of the epidemiologic data

We examined the relationship between exposure to pesticides and the subsequent development of brain tumors in adults through a critical review of the literature. The results of retrospective case-control studies are conflicting, in part because of biases in the selection of patients and controls, poor definition and ascertainment of the nature and extent of the exposure to pesticides, and a non-uniform approach to the collection of antecedent information. A number of the studies evaluated farmers as a group exposed to pesticides; however, inference about cancer incidence in farmers may reflect not only their possible exposure to pesticides, but also exposure to petrochemical products, exhaust fumes, mineral and organic dusts, and biological exposure to animals and microbes. The great majority of the cohort studies of chemical workers employed in the manufacture of pesticides did not indicate an excess of brain cancer mortality. There have been few cohort studies of pesticide applicators and these revealed elevated but non-significant relative risks for excess mortality due to brain cancer. Existing data are insufficient to conclude that exposure to pesticides is a clear risk factor for brain tumors. Given the conflicting results reported for farmers and pesticide applicators and their contrast to chemical workers, it seems more plausible that exposure to multiple agents and/or other factors, such as genetic predisposition, are most relevant with respect to brain tumor pathogenesis.

Home pesticide use and childhood cancer: a case-control study

The association between childhood cancer and home pesticide use was examined in a case-control study of children under 15 years of age. Parents of 252 children diagnosed with cancer in the Denver area between 1976 and 1983 and of 222 control subjects were interviewed regarding use of home pest extermination, yard treatment, and pest strips. The strongest associations were found for yard treatments and soft tissue sarcomas (odds ratios [ORs] around 4.0) and for use of pest strips and leukemias (ORs between 1.7 and 3.0). These results suggest that use of home pesticides may be associated with some types of childhood cancer.

Assessment of exposure to 2,4-dichlorophenoxyacetic acid in the chemical industry: results of a five year biological monitoring study

Data on individual exposure to 2,4-dichlorophenoxyacetic acid (2,4-D) in herbicide production plants are limited. Hence, the urinary excretion of this herbicide was measured during a five year (1985-1989) biological monitoring study of 27 men and 18 women employees exposed during the production and formulation of 2,4-D and related sodium and dimethylamine salts. In separate studies, specimens of urine were collected in the morning, or during the last three hours of a working shift, or over a 24 hour period (1200 to 1200 or 0800 to 0800) and were analysed by an immunochemical method (2,4-D radioimmunoassay (RIA)). Urinary 2,4-D concentrations varied within a large scale from only a few micrograms/l to several 10s of mg/l. During a week, herbicide excretion increased, culminating on Friday. At the weekend, when no work was done, 2,4-D elimination decreased but did not return to zero in any case. After an interruption of exposure for about three weeks, urinary 2,4-D was no longer detectable. About five days after restarting work, body concentrations had built up again. Measurements of 2,4-D concentrations in air at different work-places showed that herbicide concentrations did not exceed 0.5 mg/m3. As well as inhalation, dermal 2,4-D absorption seemed to play an important part in total uptake of herbicide. Furthermore, a strong correlation was found (r = 0.9628) between 2,4-D urinary concentration, adjusted for endogenous creatinine, and the estimated amount of absorbed herbicide. Estimated absorbed doses were, in most cases, well below 0.1 mg 2,4-D/kg body wt/day. Sometimes this concentration was greatly exceeded. Thyroid hormone concentrations in blood were measured as well. No notable abnormalities were found. Exposed subjects were also typed for histocompatibility locus antigens (ABC antigens). The immunochemical determination of 2,4-D in specimens of urine proved to be a simple, cost effective, and non-invasive method to measure human exposure.