On recent meta-analyses of exposure to glyphosate and risk of non-Hodgkin's lymphoma in humans

Epidemiologic studies of glyphosate and non-Hodgkin's lymphoma: A review with consideration of exposure frequency, systemic dose, and study quality

I reviewed the epidemiologic literature for glyphosate and non-Hodgkin's lymphoma (NHL) in the context of the frequency of exposure in each epidemiologic study, systemic dose from biomonitoring studies of applicators, and aspects of study quality. Nine studies were identified, 7 case control and 2 cohort, by a literature search and a review of reference lists from published studies and recent regulatory evaluations. All but one study involved exposure scenarios that were so infrequent that they are not credible for cancer causation. Most studies failed to address potential confounding from other pesticides. Only one study - the US Agricultural Health Study (AHS) - included individuals with relatively frequent exposure to glyphosate and involved comprehensive statistical analyses to address potential confounding by personal factors and other pesticide exposures. The AHS did not find an association between glyphosate and NHL, even among the most frequently exposed participants (≥ 109 days of use) (RR = 0.80, 95% CI 0.60, 1.06). These findings are consistent with observations that glyphosate systemic doses from agricultural applications are many orders of magnitude less than daily lifetime doses considered by regulatory agencies to impart no excess risk of deleterious health effects, even for sensitive subpopulations.

A simulated heat wave-but not herbicide exposure-alters resource investment strategy in an insect

Animals are increasingly exposed to potential stressors related to environmental change, and multiple stressors may alter the dynamics by which animals acquire resources and invest those resources into important life-history traits. Stress may lead to the prioritization of current reproduction to maximize lifetime reproduction (i.e., terminal investment [TI]) or, in contrast, prioritize somatic investment over current reproduction to facilitate future reproductive opportunities (i.e., reproductive restraint [RR]). Tests of the TI and RR hypotheses typically use immune challenges as stressors, and have not been explicitly tested in the context of environmental change even though warming influences resource allocation patterns across taxa. Further, the multiple-stressor framework has been a useful construct to clarify the costs of complex environmental shifts to animals, but it has not been leveraged to understand such effects on investment strategy. Thus, we tested the TI and RR hypotheses by manipulating widespread features of environmental change-glyphosate-based herbicide (GBH; Roundup®) exposure and a simulated heat wave-in the variable field cricket (Gryllus lineaticeps). A simulated heat wave affected the life-history tradeoff between investment into reproduction and soma. Specifically, heat wave prioritized investment into ovary mass over non-reproductive tissue, even after accounting for food consumption, in support of the TI hypothesis. In contrast, GBH exposure did not affect any measured trait, and crickets did not discriminate between tap water and GBH solution during drinking. Therefore, some-but not all-aspects of environmental change may alter resource investment strategies in animals. We encourage continued integration of the multiple-stressor framework and life-history theory to better understand how animals respond to their rapidly changing environments.

Pesticides in a warmer world: Effects of glyphosate and warming across insect life stages

Glyphosate (GLY) is a broad-spectrum herbicide that is the most commonly applied pesticide in terrestrial ecosystems in the U.S. and, potentially, worldwide. However, the combined effects of warming associated with climate change and exposure to GLY and GLY-based formulations (GBFs) on terrestrial animals are poorly understood. Animals progress through several life stages (e.g., embryonic, larval, and juvenile stages) that may exhibit different sensitivities to stressors. Therefore, we factorially manipulated temperature and GLY/GBF exposure in the variable field cricket (Gryllus lineaticeps) during two life stages-nymphal development and adulthood-and examined key animal traits, such as developmental rate, body size, food consumption, reproductive investment, and lifespan. A thermal environment simulating future climate warming obligated several costs to fitness-related traits. For example, warming experienced during nymphal development reduced survival, adult body mass and size, and investment into flight capacity and reproduction. Warming experienced by adults reduced lifespan and growth rate. Alternatively, the effects of GBF exposure were more subtle, often context-dependent (e.g., effects were only detected in one sex or temperature regime), and were stronger during adult exposure relative to exposure during development. There was evidence of additive costs of warming and GBF exposure to rates of feeding and growth in adults. Yet, the negative effect of GBF exposure to adult lifespan did not occur in warming conditions, suggesting that ongoing climate change may obscure some of the costs of GBFs to non-target organisms. The effects of GLY alone (i.e., in the absence of proprietary surfactants found in commercial formulations) were non-existent. Animals will be increasingly exposed to warming and GBFs, and our results indicate that GBF exposure and warming can entail additive costs for an animal taxon (insects) that plays critical roles in terrestrial ecosystems.

Using the Matrix to bridge the epidemiology/risk assessment gap: a case study of 2,4-D

BACKGROUND

The Matrix is designed to facilitate discussions between practitioners of risk assessment and epidemiology and, in so doing, to enhance the utility of epidemiology research for public health decision-making. The Matrix is comprised of nine fundamental "asks" of epidemiology studies, focusing on the types of information valuable to the risk assessment process.

OBJECTIVE

A 2,4-dichlorophenoxyacetic acid (2,4-D) case study highlights the extent to which existing epidemiology literature includes information generally needed for risk assessments and proffers suggestions that would assist in bridging the epidemiology/risk assessment gap.

METHODS

Thirty-one publications identified in the US Environmental Protection Agency 2,4-D epidemiology review were assessed. These studies focused on associations between 2,4-D exposure and non-Hodgkin lymphoma (NHL), respiratory effects, and birth outcomes.

RESULTS

Many of the papers met one or more specific elements of the Matrix. However, from this case study, it is clear that some aspects of risk assessment, such as evaluating source-to-intake pathways, are generally not considered in epidemiology research. Others are incorporated, but infrequently (e.g. dose-response information, harmonization of exposure categories). We indicated where additional analyses or modifications to future study design could serve to improve the translation.

DISCUSSION

Interaction with risk assessors during the study design phase and using the Matrix "asks" to guide the conversations could shape research and provide the basis for requests for funds to support these additional activities. The use of the Matrix as a foundation for communication and education across disciplines could produce more impactful and consequential epidemiology research for robust risk assessments and decision-making.

Exposure to glyphosate and risk of non-Hodgkin lymphoma: an updated meta-analysis

OBJECTIVE

We updated a recent systematic review and meta-analysis of epidemiologic studies to help clarifying the association between exposure to glyphosate and risk of non-Hodgkin lymphoma (NHL).

METHODS

We conducted an updated search of the literature, and identified a total of 15 relevant publications, from which we extracted results from six non-overlapping studies. We performed random-effects meta-analyses for ever-exposure to glyphosate, dose-response, and risk of specific NHL subtypes Results: The meta-RR for ever-exposure to glyphosate was 1.05 (95% confidence interval [CI] 0.90-1.24; I2 = 0%). The meta-RR for the highest category of exposure was 1.15 (95% CI 0.72-1.83; 3 studies). The meta-RR for diffuse large B-cell lymphoma (DLBCL) was 1.29 (95% CI 1.02-1.63; 4 studies), that for follicular lymphoma was 0.84 (95% CI 0.61-1.17), and that for chronic lymphocytic leukemia/small lymphocytic lymphoma was 1.33 (95% CI 0.65-2.70). There was indication of publication bias.

CONCLUSIONS

This updated meta-analysis reinforces our previous conclusion of a lack of an association between exposure to glyphosate and risk of NHL overall, although an association with DLBCL cannot be ruled out.

A systematic review and meta-analysis of occupational exposures and risk of follicular lymphoma

BACKGROUND

The etiology of follicular lymphoma (FL), a common non-Hodgkin lymphoma subtype, is largely unknown.

OBJECTIVE

We performed a systematic review and meta-analysis of observational studies examining the relationship between occupational exposures and FL risk.

METHODS

We searched Ovid MEDLINE, Ovid EMBASE, and Web of Science for eligible observational studies examining job titles or occupational exposures prior to January 1, 2020. We performed a narrative synthesis and used random-effects models to generate meta-estimates of relative risk (RR) with 95% confidence intervals (95%CI) for exposures reported by three or more studies.

RESULTS

Fifty-eight studies were eligible. Ten cohort and 37 case-control studies quantified FL risk in relation to any exposure to one or more occupational groups or agents. Eight cohort and 19 case-control studies examined dose-response relationships. We found evidence of a positive association with increasing plasma concentration of dichlorodiphenyldichloroethylene (DDE; meta-RR = 1.51, 95%CI = 0.99, 2.31; I² = 0.0%) and polychlorinated biphenyls (PCBs; meta-RR = 1.47, 95%CI = 0.97, 2.24; I² = 8.6%). We observed a positive association with exposure to any solvent (meta-RR = 1.16, 95%CI = 1.00, 1.34; I² = 0.0%) and chlorinated solvents (meta-RR = 1.35, 95%CI = 1.09, 1.68; I² = 0.0%). Single studies reported a significant positive dose-response association for exposure to any pesticide, hexachlorobenzene, any organophosphate, diazinon, metolachlor, carbaryl, lindane, trichloroethylene, oils/greases, and extremely low-frequency magnetic fields. Job title-only analyses suggested increased risk for medical doctors and spray painters, and decreased risk for bakers and teachers. Overall, studies demonstrated low risk of bias, but most studies examined small numbers of exposed cases.

CONCLUSIONS

Current evidence indicates a positive association between FL and occupational exposure to DDE, PCBs, any solvent and chlorinated solvents. Our findings may help guide policies and practices on the safe use of solvents and inform models of lymphomagenesis. Future studies with larger sample sizes and comprehensive quantitative exposure measures may elucidate other avoidable carcinogenic exposures.