Abstract

Malathion has been widely used worldwide in arbovirus control programs. In 2015, it was classified by the International Agency for Research on Cancer (IARC) as a probable carcinogen to humans. This work aimed to systematize the evidence of the carcinogenic and mutagenic effects associated with the exposure of malathion and its analogs, malaoxon and isomalathion. The search was carried out in Toxline, PubMed and Scopus databases for original papers published from 1983 to 2015. In all, 73 papers were selected from a total of 273 eligible papers. The results of in vitro and in vivo studies showed mainly genetic and chromosomal damages caused by malathion. The epidemiological studies evidenced significant positive associations for thyroid, breast, and ovarian cancers in menopausal women. This evidence of the carcinogenic effect of malathion should be considered before its use in arbovirus control programs.

Key words
Malathion; Carcinogenicity Tests; Mutagenicity Tests; Environmental Health

Introduction

Pesticides are chemical compounds used extensively in agriculture, for the chemical control of spontaneous species in urban environment and vectors, in public health campaigns¹1 Ojha A, Srivastava N. In vitro studies on organophosphate pesticides induced oxidative DNA damage in rat lymphocytes. Mutat Res Genet Toxicol Environ Mutagen 2014; 721:10-17. and are a danger to humans and nature²2 Ecobichon DJ. Pesticide use in developing countries. Toxicology 2001; 160(1-3):27-33.. Among the widely used is the group of organophosphates (OP), which are irreversible inhibitors of acetylcholinesterase (AChE), active in all animal groups that use acetylcholine as a neurotransmitter³3 Edwards FL, Tchounwou PB. Environmental toxicology and health effects associated with methyl parathion exposure - a scientific review. Int J Environ Res Public Health 2005; 2(3):430-441.. The consequent accumulation of this molecule in the body causes toxic effects on the different systems of exposed living beings, such as muscular, nervous, immune and endocrine alterations⁴4 Ecobichon DJ, Joy RM. Pesticides and neurological diseases. In: Casarett LJ, Doull J, organizadores Toxicology: the basic science of poisons. 4ª ed. Boca Raton, CRC Press; 1991. p. 565-622.

5 Cavaliere MJ, Calore EE, Perez NM, Puga FR. Miotoxicidade por organofosforados. Rev Saúde Publica 1996; 30(3):267-272.

6 Repetto R, Baliga SS. Review article: Pesticide and immunosuppression: the risks to public heath. Health Policy Plan 1997; 12(2):97-106.^-77 Koifman S, Koifman RJ, Meyer A. Human reproductive system disturbances and pesticide exposure in Brazil. Cad Saude Publica 2002; 18(2):435-445.. Among its possible chronic effects, characterized by late onset, are irreversible damages, such as paralysis and neoplasms⁸8 Peres F, Moreira JC, Dubois GS. Agrotóxicos, saúde e ambiente: uma introdução ao tema. In: Peres F, Moreira JC, organizadores. É veneno ou é remédio?Agrotóxicos, saúde e ambiente. Rio de Janeiro: Fiocruz; 2003. p. 21-41..

In Brazil, with the exponential growth of the dengue epidemic in 2015, when more than 1 million cases were confirmed⁹9 Brasil. Ministério da Saúde (MS). Secretaria de Vigilância em Saúde. Monitoramento dos casos de dengue e febre de chikungunya até a Semana Epidemiológica 48, 2015. Bol Epidemiol 2015; 46(14):1-9., and with the onset of Chikungunya fever (in 2014) and the Zika virus epidemic (in 2015), with consequences even more harmful to the population, a review of the National Aedes aegypti (transmitter mosquito) Control Program was requested, with the intensified use of larvicides and adulticides for this mosquito, going back to the 2014 guidelines regarding the use of UBV spraying with Malathion at 30% diluted in water for the whole national territory¹⁰10 Brasil. Ministério da Saúde (MS). Recomendações sobre o uso de Malathion Emulsão Aquosa - EA 44% para o controle de Aedes aegypti em aplicações espaciais a Ultra Baixo Volume (UBV) [Internet]. 2014 [acessado 2017 Mar 28]. Disponível em: http://portalarquivos.saude.gov.br/images/pdf/2014/setembro/02/Recomenda----es-para-o-uso-de-malathion-EW.pdf
http://portalarquivos.saude.gov.br/image... . This was criticized by the Brazilian Association of Public Health, which issued a technical note warning of the dangers to health and the environment¹¹11 Associação Brasileira de Saúde Coletiva (Abrasco). Nota técnica e carta aberta à população: Microcefalia e doenças vetoriais relacionadas ao Aedes aegypti - os perigos das abordagens com larvicidas e nebulização química - fumacê. GT Saúde e Ambiente [Internet]. Abrasco; 2016 [acessado 2016 Jul 10] Disponível em: https://www.abrasco.org.br/site/noticias/institucional/nota-tecnica-sobre-microcefalia-e-doencas-vetoriais-relacionadas-ao-aedes-aegypti-os-perigos-das-abordagens-com-larvicidas-e-nebulizacoes-quimicas-fumace/15929/
https://www.abrasco.org.br/site/noticias... .

Malathion (diethyl (dimethoxythiophosphorylthio) succinate) is an OP used in various food crops for the control of unwanted species and is often used in insect control¹²12 Mills PK, Yang R. Breast cancer risk in hispanic agricultural workers in California. Int J Occup Environ Health 2005; 11(2):123-131., as a commercial or technical quality product containing approximately 90-95% of the product in weight and may contain up to twelve impurities formed during manufacture and storage¹³13 Flessel P, Quintana PJ, Hooper K. Genetic toxicity of malathion: a review. Environ Mol Mutagen 1993; 22:7-17.. Among the relevant impurities are malaoxon and isomalathion, produced by oxidation¹⁴14 Thompson CW, Frick JA, Natke BC, Hansen LK. Preparation, analysis, and anticholinesterase properties of O,O-dimethyl phosphorothioate isomerides. Chem Res Toxicol 1989 ; 2:386-391. and the chemical or thermal isomerization of malathion, respectively¹⁵15 Iyer V, Parmar BS. The isomalathion problem - a review. Int J Tropic Agric 1984; 11:199-204..

Its mutagenic capacity and potential carcinogenic effect have been discussed¹⁶16 Moore PD, Yedjou CG, Tchounwou PB. Malathion-Induced Oxidative Stress, Cytotoxicity and Genotoxicity in Human Liver Carcinoma (HepG2) Cells. Environ Toxicol 2010; 25(3):221-226.

17 Moore PD, Patlolla AK, Tchounwou PB. Cytogenetic evaluation of malathion-induced toxicity in Sprague-Dawley rats. Mutat Res 2011; 725(1-2):78-82.^-1818 Ojha A, Gupta YK. Evaluation of genotoxic potential of commonly used organophosphate pesticides in peripheral blood lymphocytes of rats. Hum Exp Toxicol 2015; 34(4):390-400.. However, despite widespread use, there are surprisingly few studies on the association of malathion and cancer, most of them in North America, others in Europe, while very few have been conducted in less industrialized countries where exposure is likely to be much higher¹⁹19 International Agency for Research on Cancer (IARC). Malathion. IARC Monogr Eval Carcinog Risk Chem Hum 2016; 112:1-454.. Some authors point out their findings as something of concern since malathion has shown high levels of carcinogenic activity, as well as chemical properties that bring it closer to other notably carcinogenic substances such as aflatoxin and benzopyrene²⁰20 Pavão AC, Leão M. Riscos da carcinogênese química no controle do Aedes aegypti. In: Augusto LGS, Carneiro RM, Martins PH, organizadores. Abordagem ecossistêmica em Saúde: Ensaios para o controle de dengue. Recife: Editora Universitária; 2005. p. 213-225..

In the 1980s, malathion was considered and evaluated by the International Agency for Research on Cancer (IARC) Working Group as not classifiable as to its carcinogenicity to humans (Group 3)²¹21 International Agency for Research on Cancer (IARC). Miscellaneous pesticides. Malathion. IARC Monogr Eval Carcinog Risk Chem Hum 1983; 30:1-424.^,2222 International Agency for Research on Cancer (IARC). Overall evaluations of carcinogenicity: an updating of IARC Monographs volumes 1 to 42. IARC Monogr Eval Carcinog Risks Hum Suppl 1987 ; 7:1-440. because it concluded that there was insufficient evidence for the carcinogenicity of malathion or its metabolite malaoxon in experimental animals, and data for humans were not available at the time. However, in 2015, IARC published a new document, classifying the pesticide as a probable human carcinogen (Group 2A)¹⁹19 International Agency for Research on Cancer (IARC). Malathion. IARC Monogr Eval Carcinog Risk Chem Hum 2016; 112:1-454..

In view of the widespread use of malathion as a pesticide worldwide, both in agriculture and public health, and in view of the risks that it can bring, this work aimed to systematize the evidence of the carcinogenic and mutagenic effects associated with the exposure of this organophosphate pesticide and its analogues (malaoxon and isomalathion).

Methods

Search data

A systematic review of the literature was performed by searching scientific papers published between 1983 and 2015. The year 1983 was chosen as the starting point of the research, since the IARC²¹21 International Agency for Research on Cancer (IARC). Miscellaneous pesticides. Malathion. IARC Monogr Eval Carcinog Risk Chem Hum 1983; 30:1-424. monograph published in that year considered malathion as “not classifiable as to its carcinogenicity to humans (Group 3)”, concluding that there was insufficient evidence for the carcinogenicity of malathion or its metabolite malaoxon in animal experiments, and there were no data regarding humans.

The search was performed in the electronic databases Scopus, PubMed and Toxline (in the latter the results of PubMed were excluded), and two command groups were employed. The first, consisting of terms related to the exposure of interest (malathion, malaoxon and isomalathion), and the second containing terms related to the outcome of interest (cancer, carcinogenicity tests, carcinogens, neoplasms, mutagenesis, mutagenicity tests and mutagens). A query was made in the Medical Subject Headings (MeSH) to select the descriptors/terms used. Boolean operator “OR” was used for the combination of the terms in each group, and “AND” operator was used for the combination between the groups.

Selection of papers

We selected original studies that showed results on the carcinogenic or mutagenic effect of malathion, malaoxon and isomalathion in living beings. Review papers, dissertations and theses identified in the search were excluded. English, Portuguese and Spanish manuscripts were considered.

The papers were selected by the researchers (authors of this paper) in two stages. In the first one, two researchers read separately the title and summary of the papers for the selection of those that should be the basis of the research. Those without an abstract or insufficient information to make a decision were kept into the next step. Cases of disagreement were resolved by a third researcher.

In the second step, all papers selected that met the inclusion/exclusion criteria and those with insufficient information for decision-making were analyzed in their entirety. As in the previous stage, the data of both reviewers were again confronted, and the differences were solved by the third reviewer.

The selected manuscripts were analyzed for the extraction of the following data: authors, year of publication, journal, study design, target population, country of study population (in epidemiological studies), exposure (malathion, malaoxon, isomalathion, mixed exposure) and main results identified regarding the carcinogenic and mutagenic effect of malathion, malaoxon and isomalathion.

Search was performed between July 4 and 12, 2016. Filters were used to select the languages and the period of publication of the manuscripts in the three databases.

Results and discussion

Search returned 178 results in Scopus, 147 in PubMed and 92 in Toxline, totaling 417 papers (Figure 1). A total of 142 duplications were identified, as well as two papers published in other languages (German and Chinese), leaving out 273 papers for eligibility evaluation.

After applying the inclusion and exclusion criteria and the two-step evaluation, 73 papers were included in this study, all in English. Of these, 24 correspond to in vitro experimental studies, including mutagenicity tests and cell cultures of both animals and human beings; 24 in vivo experimental studies, including mice, rats, hamsters, birds, frogs and flies; 25 epidemiological studies, including cohorts, case-controls and cross-sectional studies (two of them with in vitro experiments as well). The results found in the in vitro experimental studies that evaluated the carcinogenic or mutagenic effect of malathion and its analogs are summarized in Chart 1.

Three studies have shown significant increases in the DNA damage of rat peripheral blood lymphocytes following exposure to malathion¹1 Ojha A, Srivastava N. In vitro studies on organophosphate pesticides induced oxidative DNA damage in rat lymphocytes. Mutat Res Genet Toxicol Environ Mutagen 2014; 721:10-17.^,1818 Ojha A, Gupta YK. Evaluation of genotoxic potential of commonly used organophosphate pesticides in peripheral blood lymphocytes of rats. Hum Exp Toxicol 2015; 34(4):390-400.^,2626 Moore PD, Patlolla AK, Tchounwou PB. Cytogenetic evaluation of malathion-induced toxicity in Sprague-Dawley rats. Mutat Res Genet Toxicol Environ Mutagen 2011; 725:78-82.. Higher frequencies of chromosomal changes in bone marrow cells of mice in a dose-dependent manner to malathion were also observed²⁶26 Moore PD, Patlolla AK, Tchounwou PB. Cytogenetic evaluation of malathion-induced toxicity in Sprague-Dawley rats. Mutat Res Genet Toxicol Environ Mutagen 2011; 725:78-82.. Besides observing the significant reduction of cell viability and the significant increase of breaks in both single and double strand DNA, Ojha and Gupta¹⁸18 Ojha A, Gupta YK. Evaluation of genotoxic potential of commonly used organophosphate pesticides in peripheral blood lymphocytes of rats. Hum Exp Toxicol 2015; 34(4):390-400. verified the formation of DPC, in time- and dose-dependent fashion after exposure of rats’ lymphocytes to malathion both individually and mixed with two other organophosphates (Chlorpyrifos and Parathion-Methyl) when compared to the control. Since DPCs correspond to toxic lesions associated with the toxicity mechanism (s) of carcinogenic compounds⁴⁵45 Tretyakova NY, Groehler IV A, Ji S. DNA-Protein Cross-links: Formation, Structural Identities, and Biological Outcomes. Acc Chem Res 2016; 48(6):1631-1644., the study shows the carcinogenic effect of malathion. The research further concludes that malathion, along with the other pesticides of the study, should generate oxidative lesions of DNA base pairs, with a genotoxic potential to alter enzyme expression.

In cultures of human peripheral blood lymphocytes exposed to malathion, results showed dose-dependent increase of chromosomal changes and sister chromatid exchanges³⁷37 Balaji M, Sasikala K. Cytogenetic effect of malathion in in vitro culture of human peripheral blood. Mutat Res 1993; 301:13-17.^,3939 Garry VF, Nelson RL, Griffith J, Harkins M. Preparation for Human Study of Pesticide Applicators: Sister Chromatid Exchanges and Chromosome Aberrations in Cultured Human Lymphocytes Exposed to Selected Fumigants. Teratog Carcinog Mutagen 1990; 10:21-29., as well as the alkylating effect of DNA-specific nucleotides³⁴34 Pluth JM, O'Neill JP, Nicklas JA, Albertini RJ. Molecular bases of hprt mutations in malathion-treated human T-lymphocytes. Mutat Res 1998; 397:137-148.. No significant changes were observed in the DNA damage of these same cells³²32 Blasiak J, Jaloszynski P, Trzeciak A, Szyfter K. In vitro studies on the genotoxicity of the organophosphorus insecticide malathion and its two analogues. Mutat Res 1999; 445:275-283. when malathion was evaluated in comparison to its two analogs, unlike malaoxon and isomalathion, which induced DNA damage in a dose-dependent fashion. The study by Blasiak et al.³²32 Blasiak J, Jaloszynski P, Trzeciak A, Szyfter K. In vitro studies on the genotoxicity of the organophosphorus insecticide malathion and its two analogues. Mutat Res 1999; 445:275-283. was the only one to evaluate the three chemical agents in the same study and concluded that the damages caused to the DNA by malaoxon are more pronounced than those caused by isomalathion.

Josse et al.²³23 Josse R, Sharanek A, Savary CC, Guillouzo A. Impact of isomalathion on malathion cytotoxicity and genotoxicity in human HepaRG cells. Chem Biol Interact 2014; 209:68-76. evaluated the effects of malathion and isomalathion individually and combined on the human liver HepaRG cell line and showed that, although isomalathion was much more cytotoxic than malathion, both substances showed similar mutagenic effects in these hepatocytes. On the other hand, Błasiak and Trzeciak³³33 Blasiak J, Trzeciak A. Single Cell Gel Electrophoresis (Comet Assay) as a Tool for Environmental Biomonitoring. An Example of Pesticides. Pol J Environ Stud 1998; 7(4):189-194. claim that DNA damage to human lymphocytes is caused by isomalathion and not by its original compound.

The results are somewhat contradictory regarding malaoxon exposure. Blasiak and Kowalik³¹31 Blasiak J, Kowalik J. Protective Action of Sodium Ascorbate against the DNA-Damaging Effect of Malaoxon. Pestic Biochem Physiol 1999; 65:110-118. found that malaoxon promoted a significant increase in the level of DNA damage in human peripheral blood lymphocytes in the Comet Assay, and was higher with increasing dose, while in the human lineage choriocarcinoma cell (JAR) assay (model acceptable for human placental cells), malathion, and not the same agent, was found to be responsible for the cytotoxic and genotoxic effects in these cells in vitro. Authors argue that metabolites of pesticides with contradictory results regarding their carcinogenic potential should be studied, since they may represent the true carcinogens⁴⁶46 Bedor CNG. Estudo do potencial carcinogênico dos agrotóxicos empregados na fruticultura e sua implicação para a vigilância da saúde [tese]. Recife: Centro de Pesquisas Aggeu Magalhães; 2008..

Malathion has also been evaluated in gene mutation tests that employ bacteria, such as the Salmonella lactam test (genotoxin detection method)³⁵35 Hour TC, Chen L, Lin JK. Comparative investigation on the mutagenicities of organophosphate, phthalimide, pyrethroid and carbamate insecticides by the Ames and lactam tests. Mutagenesis 1998; 13(2):157-166., phage-MicroScreen (a miniaturized system that uses the induction of prophylaxis in Escherichia coli X as an indicator of genetic damage)⁴¹41 Houk VS, DeMarini DM. Induction of prophage lambda by chlorinated pesticides. Mutat Res 1987; 182:193-201. and the Ames Salmonella test⁴⁰40 Pednekar MD, Gandhi SR, Netrawali MS. Evaluation of Mutagenic Activities of Endosulfan, Phosalone, Malathion, and Permethrin, Before and After Metabolic Activation, in the Ames Salmonella Test. Environ Contam Toxicol 1987; 38:925-933.. In the three studies found, the results were negative for the mutagenic activity of malathion, and no mutagenic activities of malathion were observed in the last test before or after activation of the rat liver S9 fraction in the respective non-toxic doses (33 mg/L) and 90% toxic (1650mg/L). In a literature review, Flessel et al.⁴⁷47 Flessel P, Quintana PJ, Hooper K. Genetic toxicity of malathion: a review. Environ Mol Mutagen 1993; 22(1):7-17. also observed the same results and concluded that malathion does not appear to induce timely mutations in DNA in bacterial systems.

Of the 24 in vivo experimental studies found in this systematic review, twenty performed the experiments on rats, mice or hamsters, while the others evaluated the effects of the pesticide on birds, frog and flies. Chart 2 shows the main results of these studies.

In 1984, Degraeve et al.⁷⁰70 Degraeve N, Chollet MC, Moutschen J. Evaluation of the mutagenic potential of four commercial mixtures of insecticides. Fd Che Toxic 1984; 22(8):683-687. reported that Dynafos and Phosan Plus, insecticides containing malathion in their composition, did not induce chromosomal changes in bone marrow cells, spermatogonia or primary spermatocytes, nor alterations in the dominant lethal mutation assay, after intraperitoneal injection of rats of strain Q. However, the study has no data regarding impurities, solvents, emulsions and the like in these compounds, which shows its limitation.

In the same year, these authors exposed rats from the same strain to malathion at 99% purity by ingestion of water containing small amounts of the organophosphate (8 ppm, corresponding to the highest value allowed in Belgium for pesticide residues in fruits and vegetables) five days a week for seven consecutive weeks⁶⁹69 Degraeve N, Chollet MC, Moutschen J. Cytogenetic and genetic effects of subehronic treatments with organophosphorus insecticides. Arch Toxicol 1984; 56:66-67.. Again, they did not observe a significant increase in chromosomal breaks or gaps in the same cell types from the previous work, nor in the dominant lethal mutation assay. However, there is hardly any information on the analytical technique used to search for these changes. In 1985, the group evaluated the effects on rats injected with malathion (150 mg/kg) combined with trichlorfon (50 mg/kg), and also did not show cytogenetic effects (breaks, gaps, and chromatid alterations) of the combination⁶⁸68 Degraeve N, Chollet MC, Moutschent J. Mutagenic efficiency of organophosphorus insecticides used in combined treatments. Environ Health Perspect 1985; 60:395-398..

However, of the total in vivo experimental studies found in this study, only four showed no positive association between mutagenic effects and malathion, all from the 1980s. The first three were those mentioned above, the fourth and last of them dating from 1987, which obtained negative results regarding the production of sexual chromosome losses and non-disjunction in strains of Drosophila melanogaster exposed to malathion with 50% of the active ingredient, a percentage that may have had a significant influence on the results found⁶⁶66 Velázquez A, Creus A, Xamena N, Marcos R. Lack of mutagenicity of the organophosphorus insecticide malathion in Drosophila melanogaster. Environ Mutagen 1987;9:343-348.. Since then, there have been a further 17 studies with positive results for carcinogenicity and genotoxicity of malathion, and one for malaoxon genotoxicity.

Honda and Sinha⁶⁵65 Hoda MQ, Sinha SP. Protective role of ascorbic acid and vitamin B-complex against pesticide-induced clastogeny in bone marrow cells of mice. Internat J Vit Nutr Res 1991; 61:155-158. showed a significant increase (at a level of 0.1%) in the chromatid alterations of bone marrow cells after exposure of Mus musculus rats. Swiss albino mice strains exposed to malathion evidenced bone marrow cell metaphases with various types of chromosomal alterations, and the pesticide-induced significantly higher frequency of alterations (p<0.001) in the three acute doses tested (2.5, 5 and 10mg/kg) than in control, besides increased frequencies of sister chromatid exchanges and sperm head anomalies⁵⁹59 Giria S, Prasad SB, Giri A, Sharma GD. Genotoxic effects of malathion: an organophosphorus insecticide, using three mammalian bioassays in vivo. Mutat Res 2002; 514:223-231.. Giri et al.⁵⁴54 Giri A, Giri S, Sharma GD. Malathion and Fenvalerate Induce Micronuclei in Mouse Bone Marrow Cells. Environ Mol Mutagen 2011; 52:607-613. reported the dose-dependent increased frequency of micronucleated polychromatic erythrocytes in bone marrow cells of mice of the same species after in vivo exposure to malathion at 95% purity.

Regarding the research on the carcinogenicity of malathion in in vivo experiments, the first manuscript found dated back to 1992, in which the pesticide promoted a significant increase (p<0.05) in the induction of GST-P positive focus in hepatocytes of F344 mice compared to control⁶⁴64 Hasegawa R, Ito N. Liver medium-term bioassay in rats for screening of carcinogens and modifying factors in hepatocarcinogenesis. Fd Chem Toxic 1992; 30(11):979-992.. The expression of the GST-P enzyme is usually low in fetal hepatocytes, quiescent adults or in regeneration, placenta, heart and other organs of male rats, however, hyperplastic nodules and chemically-induced liver tumors exhibit GST-P values of about 20 to 50 times and 10 to 30 times over, respectively, when compared to normal rat liver values⁷²72 Satoh K, Kitahara A, Soma Y, Inaba Y, Hatayama I, Sato K. Purification, induction, and distribution of placental glutathione transferase; a new marker enzyme for preneoplastic cells in the rat chemical hepatocarcinogenesis. Proc Natl Acad Sci 1985; 82:3964-3968.. Thus, the study suggests the possibility of malathion being a weak hepatocarcinogenic or hepatopromoting agent. On the other hand, the study by Hoshiya et al.⁶³63 Hoshiya T, Hasegawa R, Hakoi K, Cui L, Ogiso T, Cabral R, Ito N. Enhancement by non-mutagenic pesticides of GST-P positive hepatic foci dlevelopment rat initiated with diethylnitrosamine in the rat. Cancer Lett 1993; 72:59-64., also with F344 mice, concludes and states that malathion has liver tumor promoting activity.

Studies have investigated the carcinogenic effects of malathion and estrogen in virgin female rats of the Sprague-Dawley strain, individually and in combination. Calaf and Garrido⁵⁵55 Calaf GM, Garrido F. Catechol estrogens as biomarkers for mammary gland cancer. Int J Oncol 2011; 39:177-183. observed progressive changes in the mammary cell ducts of rats treated with isolated malathion compared to control after 240 days of treatment. Besides the significantly increased size (p<0.05) of ducts in the mammary gland proliferation phase of rats treated with the pesticide, Calaf and Chau⁵¹51 Calaf GM, Echiburú-Chau C. Synergistic effect of malathion and estrogen on mammary gland carcinogenesis. Oncol Rep 2012; 28:640-646. found a growing expression of the mutant p53 tumor marker protein. Several types of pre-neoplasms in the bronchiolar epithelium of rats injected with malathion have also been found, besides carcinomas in situ⁵⁷57 Echiburú-Chau C, Calaf GM. Rat lung cancer induced by malathion and estrogen. Int J Oncol 2008; 33:603-611.. In the renal tissue of malathion-exposed rats, results suggest abnormalities with signs of malignancy⁵²52 Alfaro-Lira S, Pizarro-Ortiz M, Calaf GM. Malignant Transformation of Rat Kidney Induced by Environmental Substances and Estrogen. Int J Environ Res Public Health 2012; 9:1630-1648..

In most of the previously cited studies⁵¹51 Calaf GM, Echiburú-Chau C. Synergistic effect of malathion and estrogen on mammary gland carcinogenesis. Oncol Rep 2012; 28:640-646.^,5252 Alfaro-Lira S, Pizarro-Ortiz M, Calaf GM. Malignant Transformation of Rat Kidney Induced by Environmental Substances and Estrogen. Int J Environ Res Public Health 2012; 9:1630-1648.^,5757 Echiburú-Chau C, Calaf GM. Rat lung cancer induced by malathion and estrogen. Int J Oncol 2008; 33:603-611., treatment with the combination of malathion and estrogen-induced more cellular alterations than treatments with the substances alone. Thus, the combination of pesticides found in the environment, widely used in Latin America and many other countries, and an endogenous substance, such as estrogen, has the potential to induce deleterious effects on humans, such as breast cancer, for example⁵¹51 Calaf GM, Echiburú-Chau C. Synergistic effect of malathion and estrogen on mammary gland carcinogenesis. Oncol Rep 2012; 28:640-646.. Estrogen can also be found as a pollutant in surface and groundwater, and its presence in the environment can have severe toxicological and ecotoxicological repercussions since this substance is recognized as an endocrine disrupter, associated with premature puberty, infertility and congenital malformation⁷³73 Pal A, Gin KY-H, Lin AY-C.; Reinhard M. Impacts of emerging organic contaminants on freshwater resources: review of recent occurrences, sources, fate and effects. Sci Total Environ 2010; 408:6062-6069.

74 Diamanti-Kandarakis E, Bourguignon JP, Giudice LC, Hauser R, Prins GS, Soto AM, Zoeller RT, Gore AC. Endocrine-disrupting chemicals: An Endocrine Society scientific statement. Endocr Rev 2009, 30:293-342.^-7575 Adeel M, Song X, Wang Y, Francis D, Yang Y. Environmental impact of estrogens on human, animal and plant life: A critical review. Environ Int 2017;99:107-119..

The epidemiological studies found in this systematic review are summarized in Chart 3. The types of designs obtained were eleven control case studies, eight cohorts and six cross-sectional studies, where two of these also performed in vitro experiments with human peripheral blood lymphocytes.

Most studies (n = 16) investigated the correlations between exposure to malathion and the development of cancers. Of the 25 papers, 18 were conducted in North America (12 in the U.S. and 6 in Canada), three in Europe, three in Asia and only one in Latin America (Chile). These findings corroborate the IARC manuscript, which states that very few studies on this approach have been conducted in less industrialized countries¹⁹19 International Agency for Research on Cancer (IARC). Malathion. IARC Monogr Eval Carcinog Risk Chem Hum 2016; 112:1-454..

As to the evidence of genotoxicity investigated, in a cross-sectional study with male pesticide applicators, Andreotti et al.⁷⁶76 Andreotti G, Hoppin JA, Hou L, Koutros S, Gadalla SM, Savage SA, Lubin J, Blair A, Hoxha M, Baccarelli A, Sandler D, Alavanja M, Freeman LEB. Pesticide use and relative leukocyte telomere length in the agricultural health study. PLoS ONE 2015; 10(7):e0133382. found positive associations between the recent use of malathion and the shorter telomere relative length (p = 0.03). Telomere shortening is associated with several diseases, and most studies have reported associations between telomere length and increased risk of cancer¹⁰¹101 Ma H, Zhou Z, Wei S, Liu Z, Pooley KA, Dunning AM, Svenson U, Roos G, Hosgood HD 3rd, Shen M, Wei Q. Shortened telomere length is associated withincreased risk of cancer: a meta-analysis. PLoS One 2011; 6:e20466.^,102102 Wentzensen IM, Mirabello L, Pfeiffer RM, Savage SA. The association of telomere length and cancer: a meta-analysis. Cancer Epidemiol Biomarkers Prev 2011; 20(6):1238-1250..

In a prospective cohort with patients who attempted suicide by self-poisoning with drugs or insecticides, temporary but significant increases in peripheral blood leukocyte aneuploidy (6.3%, p < 0.01) and chromatid (5.3%, p < 0.01) and chromosomic (1.4%, p < 0.01) alteration rates after intoxication with malathion⁹⁷97 Czeizel AE. Phenotypic and cytogenetic studies in self-poisoned patients. Mutat Res 1994; 313:175-181. were observed. Also, one of 14 people poisoned by organophosphate died.

Only one of the epidemiological manuscripts addressing the mutagenic effects of malathion and complex mix of pesticides including the organophosphate did not find a positive association⁹⁵95 Titenko-Holland N, Windham G, Kolachana P, Reinisch F, Parvatham S, Osorio AM, Smith MT. Genotoxicity of malathion in human lymphocytes assessed using the micronucleus assay in vitro and in vivo: A study of malathion-exposed workers. Mutat Res 1997; 388:85-95.. This work was carried out both with a cross-sectional epidemiological study of workers exposed to pesticides and with in vitro experimentation of human peripheral blood lymphocytes also concluded that malathion has a relatively low potential to cause chromosomal damage in vitro, and the corresponding doses used in the experiment were much higher than those that professional applicators are likely to be exposed to in vivo.

On the other hand, a cross-sectional study with a worker occupationally exposed to pesticides (primarily malathion and phosphine) for more than five years, and an experimental in vitro study with human peripheral blood lymphocytes exposed to malathion revealed that the mutagenicity of malathion can be detected at a molecular level⁹⁶96 Pluth JM, Nicklas JA, O'Neill JP, Albertini RJ. Increased frequency of specific genomic deletions resulting from in vitro malathion exposure. Cancer Res 1996; 56:2393-2399.. Molecular changes in the hprt assay were observed at doses of malathion that did not produce in vitro cytotoxicity (≤50 mg/ml) and at exposure levels experienced by the individual from which the in vivo mutant was retrieved. The authors state that alterations similar to those reflected in the hprt in this study may also occur in other loci, especially oncogene or tumor suppressor genes sites, and may play a role in inducing malignancies in individuals exposed to this or a similar agent.

In epidemiological studies where exposure to complex mixtures of pesticides or combinations including malathion was found, all results found positive associations with genotoxic effects⁷⁷77 Arshad M, Siddiqa M, Rashid S, Hashmi I, Awan MA, Ali MA. Biomonitoring of toxic effects of pesticides in occupationally exposed individuals. Saf Health Work 2015; 7:156-160.^,9292 Zeljezic D, Garaj-Vrhova V. Sister chromatid exchange and proliferative rate index in the longitudinal risk assessment of occupational exposure to pesticides. Chemosphere 2002; 46:295-303.^,9393 Garaj-Vrhovac V, Zeljezic D. Cytogenetic monitoring of croatian population occupationally exposed to a complex mixture of pesticides. Toxicology 2001; 165:153-162.^,9999 Rupa DS, Reddy PP, Sreemannarayana K, Reddi OS. Frequency of sister chromatid exchange in peripheral lymphocytes of male pesticide applicators. Environ Mol Mutagen 1991; 18:136-138.^,100100 Rupa DS, Reddy PP, Reddi OS. Frequencies of chromosomal aberrations in smokers exposed to pesticides in cotton fields. Mutat Res 1989; 222:37-41. and carcinogenic effect⁸⁷87 Hohenadel K, Harris SA, McLaughlin JR, Spinelli JJ, Pahwa P, Dosman JA, Demers PA, Blair A. Exposure to multiple pesticides and risk of non-hodgkin lymphoma in men from six canadian provinces. Int J Environ Res Public Health 2011; 8:2320-2330.. Investigations of pesticides focused on the potential effects of these substances on an individual basis aim to facilitate the analysis and direct public policies. However, although multiple exposures hinder the assessment of the relationships between pesticides and their mutagenic or carcinogenic effect, they more accurately reflect how these compounds are used⁸⁷87 Hohenadel K, Harris SA, McLaughlin JR, Spinelli JJ, Pahwa P, Dosman JA, Demers PA, Blair A. Exposure to multiple pesticides and risk of non-hodgkin lymphoma in men from six canadian provinces. Int J Environ Res Public Health 2011; 8:2320-2330..

Among the manuscripts that sought to investigate correlations between malathion exposure and development of different types of cancers, five of them did not find significant positive associations in cases of non-Hodgkin’s lymphoma (NHL)⁷⁹79 Alavanja MCR, Hofmann JN, Lynch CF, Hines CJ, Barry KH, Barker J, Buckman DW, Thomas K, Sandler DP, Hoppin JA, Koutros S, Andreotti G, Lubin JH, Blair A, Freeman LEB. Non-hodgkin lymphoma risk and insecticide, fungicide and fumigant use in the agricultural health study. PLoS ONE 2014; 9(10):e109332.^,9191 Bonner MR, Coble J, Blair A, Freeman LEB, Hoppin JA, Sandler DP, Alavanja MCR. Malathion exposure and the incidence of cancer in the Agricultural Health Study. Am J Epidemiol 2007; 166(9):1023-103., multiple myeloma⁸²82 Kachuri L, Demers PA, Blair A, Spinelli JJ, Pahwa M, McLaughlin JR, Pahwa P, Dosman JA, Harris SA. Multiple pesticide exposures and the risk of multiple myeloma in Canadian men. Int J Cancer 2013; 133:1846-1858., prostate cancer⁸⁵85 Barry KH, Koutros S, Berndt SI, Andreotti G, Hoppin JA, Sandler DP, Burdette LA, Yeager M, Freeman LEB, Lubin JH, Ma X, Zheng T, Alavanja MCR. Genetic variation in base excision repair pathway genes, pesticide exposure, and prostate cancer risk. Environ Health Perspect 2011; 119(12):1726-1732.^,9191 Bonner MR, Coble J, Blair A, Freeman LEB, Hoppin JA, Sandler DP, Alavanja MCR. Malathion exposure and the incidence of cancer in the Agricultural Health Study. Am J Epidemiol 2007; 166(9):1023-103., soft tissue sarcoma⁸⁶86 Pahwa P, Karunanayake CP, Dosman JA, Spinelli JJ, McLaughlin JR, Cross-Canada Group. Soft-tissue sarcoma and pesticides exposure in men results of a canadian case-control study. J Occup Environ Med 2011; 53(11):1279-1286., combined lymphatic-hematopoietic cancers, leukemia, lung, colon and rectum, kidney and bladder cancer, and melanoma⁹¹91 Bonner MR, Coble J, Blair A, Freeman LEB, Hoppin JA, Sandler DP, Alavanja MCR. Malathion exposure and the incidence of cancer in the Agricultural Health Study. Am J Epidemiol 2007; 166(9):1023-103.. Another three found significant inverse associations between the use of organophosphate and the appearance of NHL⁷⁸78 Lerro, Koutros S, Andreotti G, Friesen MC, Alavanja MC, Blair A, Hoppin JA, Sandler DP, Lubin JH, Ma X, Zhang Y, Freeman LEB. Organophosphate insecticide use and cancer incidence among spouses of pesticide applicators in the Agricultural Health Study. Occup Environ Med 2015; 72:736-744.^,8484 Pahwa M, Harris SA, Hohenadel K, McLaughlin JR, Spinelli JJ, Pahwa P, Dosman JA and Blair A. Pesticide use, immunologic conditions, and risk of non-Hodgkin lymphoma in Canadian men in six provinces. Int J Cancer 2012; 131:2650-2659. and pancreatic cancer⁹⁰90 Andreotti G, Freeman LEB, Hou L, Coble J, Rusiecki J, Hoppin JA, Silverman DT, Alavanja MCR. Agricultural pesticide use and pancreatic cancer risk in the Agricultural Health Study Cohort. Int J Cancer 2009; 124:2495-2500..

The other half of them obtained positive associations at statistically significant levels for thyroid cancer⁷⁸78 Lerro, Koutros S, Andreotti G, Friesen MC, Alavanja MC, Blair A, Hoppin JA, Sandler DP, Lubin JH, Ma X, Zhang Y, Freeman LEB. Organophosphate insecticide use and cancer incidence among spouses of pesticide applicators in the Agricultural Health Study. Occup Environ Med 2015; 72:736-744., ovarian cancer in menopausal women⁷⁸78 Lerro, Koutros S, Andreotti G, Friesen MC, Alavanja MC, Blair A, Hoppin JA, Sandler DP, Lubin JH, Ma X, Zhang Y, Freeman LEB. Organophosphate insecticide use and cancer incidence among spouses of pesticide applicators in the Agricultural Health Study. Occup Environ Med 2015; 72:736-744., prostate cancer⁸⁰80 Koutros S, Berndt SI, Barry KH, Andreotti G, Hoppin JA, Sandler DP, Yeager M, Burdett LA, Yuenger J, Alavanja MCR, Freeman LEB. Genetic susceptibility loci, pesticide exposure and prostate cancer risk. PLoS ONE 2013; 8(4):e58195.^,8888 Band PR, Abanto Z, Bert J, Lang B, Fang R, Gallagher RP, Le ND. Prostate cancer risk and exposure to pesticides in british columbia farmers. Prostate 2011;71:168-183. and its aggressive type⁸³83 Koutros S, Freeman LEB, Lubin JH, Heltshe SL, Andreotti G, Barry KH, DellaValle CT, Hoppin JA, Sandler DP, Lynch CF, Blair A, Alavanja MCR. Risk of total and aggressive prostate cancer and pesticide use in the Agricultural Health Study. Am J Epidemiol 2012; 177(1):59-74., breast cancer⁸¹81 Cabello G, Valenzuela-Estrada M, Siques P, Brito J, Parra E, Valdivia U, Lavin C, Manríquez A, Ortega A. Relation of breast cancer and malathion aerial spraying in Arica, Chile. Int J Morphol 2013; 31(2):640-645., NHL⁹⁴94 McDuffie HH, Pahwa P, McLaughlin JR, Spinelli JJ, Fincham S, Dosman JA, Robson D, Skinnider LF, Choi NW. Non-hodgkin's lymphoma and specific pesticide exposures in men: cross-Canada study of pesticides and health. Cancer Epidemiol Biomarkers Prev 2001; 10:1155-1163.^,9898 Cantor KP, Blair A, Everett G, Gibson R, Burmeister LF, Brown LM, Schuman L, Dick FR. Pesticides and other agricultural risk factors for non-hodgkin's lymphoma among men in Iowa and Minnesota. Cancer Res 1992; 52:2447-2455. and between body mass index and cancer colonization among men who used malathion⁸⁹89 Andreotti G; Hou L; Freeman LEB; Mahajan R; Koutros S; Coble J; Lubin J; Blair A; Hoppin JA; Alavanja M. Body mass index, agricultural pesticide use, and cancer incidence in the Agricultural Health Study cohort. Cancer Causes Control 2010; 21:1759-1775..

In Chile, about 33 years after the first malathion spraying on the city of Arica, Cabello et al.⁸¹81 Cabello G, Valenzuela-Estrada M, Siques P, Brito J, Parra E, Valdivia U, Lavin C, Manríquez A, Ortega A. Relation of breast cancer and malathion aerial spraying in Arica, Chile. Int J Morphol 2013; 31(2):640-645. conducted a case-control study with women living in the city and women from Iquique, a control city where spraying had never occurred. The authors observed that those with the most extended exposure to malathion were 5.7 times more likely to be diagnosed with breast cancer, besides 30.5% of the cases of metastases found in the exposed group, compared to 16% in the never exposed group (p < 0.05). The study concluded that the increased breast cancer mortality rate in the city of Arica has a significant correlation with exposure to malathion sprayed for more than three decades.

Of all the studies included in this systematic review, only one was carried out in Brazil⁵⁸58 R´eus GZ, Valvassori SS, Nuernberg H, Comim CM, Stringari RB, Padilha PT, Leffa DD, Tavares P, Dagostim G, Paula MMS, Andrade VM, Quevedo J. DNA damage after acute and chronic treatment with malathion in rats. J Agric Food Chem 2008; 56:7560-7565., which evidences the lack of research regarding the carcinogenic and genotoxic effects of malathion in the country. On the other hand, the use of pesticides, especially in developing countries, has grown over the years, making it necessary to carry out further studies on occupational and environmental exposure to these pesticides¹⁰³103 Kós MI, Hoshino AC, Asmus CIF, Mendonça R, Meyer A. Efeitos da exposição a agrotóxicos sobre o sistema auditivo periférico e central: uma revisão sistemática. Cad Saude Publica 2013; 29(8):1491-1506..

The Brazilian Association of Collective Health (ABRASCO) has produced a Technical Note¹¹11 Associação Brasileira de Saúde Coletiva (Abrasco). Nota técnica e carta aberta à população: Microcefalia e doenças vetoriais relacionadas ao Aedes aegypti - os perigos das abordagens com larvicidas e nebulização química - fumacê. GT Saúde e Ambiente [Internet]. Abrasco; 2016 [acessado 2016 Jul 10] Disponível em: https://www.abrasco.org.br/site/noticias/institucional/nota-tecnica-sobre-microcefalia-e-doencas-vetoriais-relacionadas-ao-aedes-aegypti-os-perigos-das-abordagens-com-larvicidas-e-nebulizacoes-quimicas-fumace/15929/
https://www.abrasco.org.br/site/noticias... warning about products such as malathion, among others, currently used in vector control of arboviruses, since the real damages caused to the environment and human health have not yet been adequately studied or revealed to vulnerable populations, including Public Health workers. Its harmful effects have been disregarded both in the aggravation of viruses and in the emergence of other pathologies such as allergies, immunotoxicity, cancer, hormonal disorders, neurotoxicity, among others¹¹11 Associação Brasileira de Saúde Coletiva (Abrasco). Nota técnica e carta aberta à população: Microcefalia e doenças vetoriais relacionadas ao Aedes aegypti - os perigos das abordagens com larvicidas e nebulização química - fumacê. GT Saúde e Ambiente [Internet]. Abrasco; 2016 [acessado 2016 Jul 10] Disponível em: https://www.abrasco.org.br/site/noticias/institucional/nota-tecnica-sobre-microcefalia-e-doencas-vetoriais-relacionadas-ao-aedes-aegypti-os-perigos-das-abordagens-com-larvicidas-e-nebulizacoes-quimicas-fumace/15929/
https://www.abrasco.org.br/site/noticias... .

Conclusion

This systematic returned results that evidenced the mutagenic effect of malathion used as a commercial formulation, that is, containing its analogs malaoxon and isomalathion, and its ability to promote changes in DNA in vivo. Thus, neoplastic processes can be triggered both in animals and in exposed humans once such changes can reach regions of oncogenes or tumor suppressors in the DNA.

The results of the in vitro studies in both animal and human cell cultures exposed to malathion showed DNA damage, chromosomal alterations, sister chromatid exchanges and micronuclei. In vivo experimental studies have shown sufficient evidence regarding the potential of the pesticide both in inducing genetic damage and inducing neoplasms in mammals. Epidemiological studies have shown statistically significant positive associations for thyroid, breast, and ovarian cancer in menopausal women.

The carcinogenic effect of this pesticide and its implications on the environment and humans should be considered, particularly in the context of arbovirus control.

References

Publication Dates

History