Evaluation of phosphine genotoxicity at occupational levels of exposure in New South Wales, Australia

DNA damage and epigenetic alteration in soybean farmers exposed to complex mixture of pesticides

Exposure to pesticides can trigger genotoxic and mutagenic processes through different pathways. However, epidemiological studies are scarce, and further work is needed to find biomarkers sensitive to the health of exposed populations. Considering that there are few evaluations of soybean farmers, the aim of this study was to assess the effects of human exposure to complex mixtures of pesticides. The alkaline comet assay modified with restriction enzyme (hOGG1: human 8-oxoguanine DNA glycosylase) was used to detect oxidised guanine, and compared with the buccal micronucleus cytome assay, global methylation, haematological parameters, biochemical analyses (serum glutamic oxaloacetic transaminase, serum glutamic pyruvic transaminase, gamma-glutamyl-transferase and butyrylcholinesterase), and particle-induced X-ray emission (PIXE) for the analysis of inorganic elements. Farm workers (n = 137) exposed to different types of pesticides were compared with a non-exposed reference group (control; n = 83). Results of the enzyme-modified comet assay suggest oxidation of guanine in DNA generated by pesticides exposure. It was observed that DNA damage (comet assay and micronucleus test) was significantly increased in exposed individuals compared to the unexposed group. The micronucleus test demonstrated elimination of nuclear material by budding, defective cytokinesis and dead cells. Occupationally exposed individuals also showed genomic hypermethylation of DNA, which correlated with micronucleus frequency. No differences were detected regarding the haematological and biochemical parameters. Finally, significantly higher concentrations of Al and P were observed in the urine of the soybean farmers. DNA damage could be a consequence of the ability of the complex mixture, including Al and P, to cause oxidative damage. These data indicate that persistent genetic instability associated with hypermethylation of DNA in soybean workers after long-term exposure to a low-level to pesticides mixtures may be critical for the development of adverse health effects such as cancer.

The use of the lymphocyte cytokinesis-block micronucleus assay for monitoring pesticide-exposed populations

Pesticides are widely used around the world, and hundreds of millions of people are exposed annually in occupational and environmental settings. Numerous studies have demonstrated relationships between pesticide exposure and increased risk of cancers, neurodegenerative and neurodevelopmental disorders, respiratory diseases and diabetes. Assessment of genotoxicity of pesticides and biomonitoring their effect in exposed populations is critical for a better regulation and protection, but it can be complicated because pesticides are often used as complex mixtures. The cytokinesis-block micronucleus assay in human lymphocytes (L-CBMN) is a validated method of assessment of DNA damage induced by clastogenic and aneuploidogenic mechanisms. The goal of this review is to provide an updated summary of publications on biomonitoring studies using this assay in people exposed to pesticides in different settings, and to identify gaps in knowledge, and future directions. A literature search was conducted through MedLine/PubMed and TOXLINE electronic databases up to December 2015. A total of 55 full-text articles, related to 49 studies, excluding reviews, were selected for in depth analysis, divided by the settings where exposures occurred, such as chemical plant workers, pesticide sprayers, floriculturists, agricultural workers and non-occupationally exposed groups. Majority of studies (36 out of 49) reported positive findings with L-CBMN assay. However, most of the studies of professional applicators that used single pesticide or few compounds in the framework of specific programs did not show significant increases in MN frequency. A decreased level of pesticide-induced genotoxicity was associated with the proper use of personal protection. In contrast, subjects working in greenhouses or during intensive spraying season and having acute exposure, showed consistent increases in MN frequency. Overall, this analysis confirmed that L-CBMN is an excellent tool for pesticide biomonitoring, and can validate the effects of educational and intervention programs on reducing exposure and genetic damage.

Aluminium phosphide-induced genetic and oxidative damages in vitro: attenuation by Laurus nobilis L. leaf extract

Objective:

The present investigation was undertaken to assess the protective effect of Laurus nobilis leaf extract (LNE) against aluminum phosphide (AIP)-induced genotoxic and oxidative damages stress in cultured human blood cells in the presence of a metabolic activator (S9 mix).

Materials and Methods:

Sister chromatid exchange (SCE) and chromosome aberration (CA) assays were used to assess AlP-induced genotoxicity and to establish the protective effects of LNE. In addition, we determined total antioxidant capacity (TAC) and total oxidative status (TOS) levels in AlP and LNE treated cultures for biomonitoring the oxidative alterations.

Results:

There was significant increases (P < 0.05) in both SCE and CA frequencies of cultures treated with AlP as compared to controls. Our results also showed that AlP (58 mg/l) caused oxidative stress by altering TAC and TOS levels. However, co-application of LNE (25, 50, 100 and 200 mg/l) and AlP resulted in decreases of SCE, CA rates and TOS level and increases of TAC level as compared to the group treated with AlP alone.

Conclusion:

The preventive role of LNE in alleviating AlP-induced DNA and oxidative damages was indicated for the first time in the present study.

Aluminum phosphide-induced genetic and oxidative damages in rats: attenuation by Laurus nobilis leaf extract

Aluminum phosphide (AlP) is a colorless, flammable, liquefied pesticide that is commonly used to control insects, nematodes, weeds, and pathogens in crops, forests, ornamental nurseries, and wood products. Early investigations of AlP-poisoned mammalian cells led to the proposed involvement of oxidative damage in its toxicity mechanism. Therefore, this study was aimed to evaluate the effect of Laurus nobilis (L) leaf extract (LNE) against AlP-induced genetic and oxidative damages in rats. Selected animals were assigned to four groups (n = 6), namely, group A: control (only distilled water is injected); group B: AlP (4 mg kg(-1) injected intraperitoneally (i.p.)); group C: LNE (200 mg kg(-1) injected i.p.), and group D: AlP plus LNE, respectively. The experimental period lasted for 14 successive days. Chromosomal aberrations (CAs) and micronucleus (MN) assay were used for monitoring genotoxic damage. In addition, biochemical parameters such as total antioxidant capacity (TAC) and total oxidative status (TOS) were examined in serum samples to determine oxidative damage. Our results indicated that AlP caused increase in CA and MN assay rates and alterations in TAC and TOS levels when compared with control group. On the contrary, LNE did not change the rates of both the analyzed cytogenetic end points and led to increase in TAC level. Moreover, we observed that LNE suppressed the genetic damage by AlP to bone marrow cells in vivo. Interestingly AlP-induced oxidative stress was also strongly reduced by LNE. The results of the present study indicated that the protective effect of LNE might be ascribable to its antioxidant and free radical scavenging properties.

Micronuclei and pesticide exposure

Micronucleus (MN) is a biomarker widely used in biomonitoring studies carried out to determine the genetic risk associated to pesticide exposure. Many in vitro and in vivo studies, as well as epidemiological approaches, have demonstrated the ability of certain chemical pesticides to produce genetic effects including cancer and other chronic pathologies in humans; thus, biomonitoring studies have been carried out to characterise the genetic risk associated to pesticide exposure. It must be noted that 'pesticide exposure' is a broad term covering complex mixtures of chemicals and many variables that can reduce or potentiate their risk. In addition, there are large differences in pesticides used in the different parts of the world. Although pesticides constitute a wide group of environmental pollutants, the main focus on their risk has been addressed to people using pesticides in their working places, at the chemical industry or in the crop fields. Here, we present a brief review of biomonitoring studies carried out in people occupationally exposed to pesticides and that use MN in lymphocytes or buccal cells as a target to determine the induction of genotoxic damage. Thus, people working in the chemical industry producing pesticides, people spraying pesticides and people dedicated to floriculture or agricultural works in general are the subject of specific sections. MN is a valuable genotoxic end point when clear exposure conditions exist like in pesticide production workers; nevertheless, better study designs are needed to overcome the uncertainty in exposure, genetic susceptibility and statistical power in the studies of sprayers and floriculture or agricultural workers.

Worker exposure standard for phosphine gas

The 1998 U.S. Environmental Protection Agency Office of Pesticide Programs (OPP) re-registration eligibility decision (RED) for phosphine fumigants has generated much interest in defining safe levels of exposure for workers and worker bystanders. This report summarizes the pertinent literature on phosphine toxicity, including animal inhalation studies and human epidemiology studies, and also describes a margin-of-exposure (MOE) analysis based on available worker exposure data. In addition, a safe occupational exposure limit is estimated using typical OPP assumptions, after determination of appropriate uncertainty factors, based on quality of data in the principal study and pharmacokinetic considerations. While a conservative 8-hour time-weighted average (TWA) of 0.1 ppm was calculated, the overall weight of evidence, from a risk-management perspective, supports a conclusion that an occupational TWA of 0.3 ppm provides adequate health protection. In addition, a 15-minute short-term exposure limit (STEL) of 3 ppm was estimated. Finally, in contrast to the MOE analysis described in the OPP's phosphine RED, the MOE analysis described herein does not indicate that fumigation workers are currently being exposed to unacceptable levels of phosphine. Collectively, these findings support the occupational exposure limits of 0.3 ppm (8-hour TWA) and 1 ppm (STEL) established in the updated applicator's manuals for phosphine-generating products, which recently received approval from OPP.

Genotoxicity of pesticides: a review of human biomonitoring studies

Pesticides constitute a heterogeneous category of chemicals specifically designed for the control of pests, weeds or plant diseases. Pesticides have been considered potential chemical mutagens: experimental data revealed that various agrochemical ingredients possess mutagenic properties inducing mutations, chromosomal alterations or DNA damage. Biological monitoring provides a useful tool to estimate the genetic risk deriving from an integrated exposure to a complex mixture of chemicals. Studies available in scientific literature have essentially focused on cytogenetic end-points to evaluate the potential genotoxicity of pesticides in occupationally exposed populations, including pesticide manufacturing workers, pesticide applicators, floriculturists and farm workers. A positive association between occupational exposure to complex pesticide mixtures and the presence of chromosomal aberrations (CA), sister-chromatid exchanges (SCE) and micronuclei (MN) has been detected in the majority of the studies, although a number of these failed to detect cytogenetic damage. Conflicting results from cytogenetic studies reflect the heterogeneity of the groups studied with regard to chemicals used and exposure conditions. Genetic damage associated with pesticides occurs in human populations subject to high exposure levels due to intensive use, misuse or failure of control measures. The majority of studies on cytogenetic biomarkers in pesticide-exposed workers have indicated some dose-dependent effects, with increasing duration or intensity of exposure. Chromosomal damage induced by pesticides appears to have been transient in acute or discontinuous exposure, but cumulative in continuous exposure to complex agrochemical mixtures. Data available at present on the effect of genetic polymorphism on susceptibility to pesticides does not allow any conclusion.

Multi-endpoint biological monitoring of phosphine workers

The pesticide phosphine (PH(3)) is a suspected carcinogen and a known clastogen which has been shown to produce chromosome damage in agricultural workers. To confirm and extend these results we evaluated 22 phosphine appliers and 26 controls matched for age and smoking status. Two independent methods were used to evaluate exposure: fluorescence in situ hybridization (FISH) with whole-chromosome paints of chromosomes 1, 2, and 4 labeled in a single color to quantify translocations in peripheral lymphocytes, and the glycophorin A (GPA) assay to quantify phenotypically mutant (NØ or NN) erythrocytes. No differences in the frequency of translocations were found in the phosphine appliers compared to the controls, and no effect of cigarette smoking was observed. However, a significant increase in the frequency of translocations with age (P<0.0001) was seen. No effect of phosphine exposure or cigarette smoking was observed in the GPA assay. These results are in contrast to previous findings from this same population which showed an increase in chromosome aberrations among phosphine appliers. The results are most easily interpreted as supporting the effectiveness of the personal protective equipment that is now worn by the workers but which was not employed prior to and during the earlier studies.

Phosphine-induced oxidative damage in rats: role of glutathione

Phosphine (PH(3)), generated from aluminium, magnesium and zinc phosphide, is a widely used pesticide. PH(3) induces oxidative stress in insects, mammalian cells, animals, and humans. The involvement of glutathione (GSH) in PH(3)-induced oxidative toxicity is controversial. GSH levels in various tested tissues were reduced in aluminium phosphide-poisoned rats and humans, while the levels remained unchanged in insects and mammalian cells. This study examines the effectiveness of endogenous GSH as a protective agent against PH(3)-induced oxidative damage in rats. The association of PH(3)-induced nephrotoxicity and cardiotoxicity with free radical production was also tested. Male Wistar rats, administered intraperitoneally (I.P.) with PH(3) at 4 mg/kg, were evaluated 30 min after treatment for PH(3) toxicity to organs. PH(3) significantly decreased GSH, GSH peroxidase and catalase, while significantly increased lipid peroxidation (as malondialdehyde and 4-hydroxyalkenals), DNA oxidation (as 8-hydroxydeoxyguaonsoine) and superoxide dismutase (SOD) levels in kidney and heart. These changes were significantly alleviated by melatonin (10 mg/kg I.P., 30 min before PH(3)), with the exception of SOD activity in heart tissue. The study also found that buthionine sulfoximine (1 g/kg I.P., 24 h before PH(3)) significantly enhanced the effect of PH(3) on GSH loss and lipid peroxidation elevation in lung. These findings indicate that (1) endogenous GSH plays a crucial role as a protective factor in modulating PH(3)-induced oxidative damage, and (2) PH(3) could injure kidney and heart (as noted earlier with brain, liver and lung) via oxidative stress and the antioxidant melatonin effectively prevents the damage.

Biological formation of volatile phosphorus compounds

Phosphine and phosphides are reported to occur at numerous environmental sites such as fresh and marine sediments, landfills, faecal matter, biogas digesters and soils. The concentrations are several log units lower than the time-weighted average exposure standard, i.e. in the order of ng per m3 of gas or ng per kg material. Research about the biological formation of highly reduced gaseous phosphorus compounds dates back more than a hundred years. The early reports had to deal with a lot of scepticism. Thanks to new analytical tools (gas chromatography) it has become clear, during the last decade, that phosphine is a global constituent of the atmosphere. Pure strains of micro-organisms cultivated under highly anaerobic conditions were shown to produce phosphine. Thermodynamic considerations indicate that it is very improbable that the reduction of phosphate to phosphine is endergonic. Therefore the generation of phosphine cannot be compared with sulphidogenesis and methanogenesis. There seems to be a link between the existence of highly reactive gaseous phosphorus compounds and increased levels of metal corrosion. The reactive compounds could be formed by micro-organisms or they are liberated from phosphorus-containing impurities in the iron by the action of bacterial metabolites. The biochemical pathways responsible for the production of gaseous phosphorus compounds have not been characterised yet.

Phosphine-induced oxidative damage in rats: attenuation by melatonin

Phosphine (PH(3)), from hydrolysis of aluminum, magnesium and zinc phosphide, is an insecticide and rodenticide. Earlier observations on PH(3)-poisoned insects, mammals and a mammalian cell line led to the proposed involvement of oxidative damage in the toxic mechanism. This investigation focused on PH(3)-induced oxidative damage in rats and antioxidants as candidate protective agents. Male Wistar rats were treated ip with PH(3) at 2 mg/kg. Thirty min later the brain, liver, and lung were analyzed for glutathione (GSH) levels and lipid peroxidation (as malondialdehyde and 4-hydroxyalkenals) and brain and lung for 8-hydroxydeoxyguanosine (8-OH-dGuo) in DNA. PH(3) caused a significant decrease in GSH concentration and elevation in lipid peroxidation in brain (36-42%), lung (32-38%) and liver (19-25%) and significant increase of 8-OH-dGuo in DNA of brain (70%) and liver (39%). Antioxidants administered ip 30 min before PH(3) were melatonin, vitamin C, and beta-carotene at 10, 30, and 6 mg/kg, respectively. The PH(3)-induced changes were significantly or completely blocked by melatonin while vitamin C and beta-carotene were less effective or inactive. These findings establish that PH(3) induces and melatonin protects against oxidative damage in the brain, lung and liver of rats and suggest the involvement of reactive oxygen species in the genotoxicity of PH(3).

Clinical evaluation of pesticide exposure and poisonings

Pesticide exposures cause disorders varying from straightforward topical irritant reactions, such as those to synthetic pyrethroid insecticides, to complex systemic illness, such as that resulting from cholinesterase inhibition by organophosphate pesticides. The acute illness syndromes associated with pesticides most commonly encountered by clinicians are illustrated here by cases reported to the California Pesticide Illness Surveillance Program. The issues raised include asthma associated with exposure to contaminants in organophosphate insecticides, systemic toxicity of ingested pyrethroids (in children), and illnesses associated with spills or misuse of fumigants.