Pesticides, endocrine disruptors

But if we take into account the emerging pollutants and compounds, the choice of which is guided by environmental considerations (mainly risks for health), then surfactants, endocrine disruptors, pesticides, other industrial organics (PAH, aromatic amines,...) or inorganics (sulphides, arsenic,...) and microbiological indicators (pathogens) must also be considered. 

Blizard, D., Sueyoshi, T., Negishi, M., Dehal, S. S., and Kupfer, D. (2001) Mechanism of induction of cytochrome p450 enzymes by the proestrogenic endocrine disruptor pesticide-methoxychlor interactions of methoxychlor metabolites with the constitutive androstane receptor system. Drug Metab. Dispos. 29 (6), 781-785. 

Endocrine disruptors apparently affect all nuclear receptors. Thus, a notable increment in impotence, alterations of the libido and of oligospermia in workers exposed to pesticides has been described. These alterations are due to the action of some compounds with estrogen-mimetic action and to their interaction with the androgen receptor. Additionally, alterations of thyroid function have been detected in rats exposed to dioxin and other toxic agents,... 

H.A. Tilson, Developmental neurotoxicity of endocrine disruptors and pesticides. Identification of important gaps and research needs. Environ. Health Perspect. 106 807, 1998. 

An overview of the literature shows that in the majority of cases, CA did yield accurate predictions of combination effects, even with mixtures composed of chemicals that operate by diverse modes of action. The studies available were dealing with mixtures of chemicals having an unspecific mode of action (membrane disturbance or narcosis) or with pesticides, mycotoxins, or endocrine disruptors. In ecotoxicol-ogy, CA usually produced more conservative predictions than IA. There are indications that this is true also for mammalian toxicology, but more data are needed to come to more definitive conclusions. The validity of CA or IA was confirmed for individual-based endpoints like growth or reproduction, but also for effects at the cellular or subcellular level and for community-based endpoints. 

As we have seen, there are many other chemicals capable of causing these effects, although they are generally very much less potent that the natural oestrogens and the synthetic oestrogens used in the contraceptive piU. Mixtures of these chemicals, which includes natural substances from plants, pesticides, and industrial chemicals, may be more potent than the individual components. This phenomenon is called synergy (see p. 35) and is currently an area of intense scientific interest, as is the subject of endocrine disruptors. 

Chemicals known to be human endocrine disruptors include dioxin, PCBs, DDT and other pesticides, diethylstilbestrol, some phthalate ester plasticizers, and heavy metals. Table 4.4 lists the EDCs. 

Amphibian endocrine disruption is of special interest to humans. The estrogen found in the painted turtle is identical to that found circulating in the human bloodstream and the endocrine disruptors that threaten wildlife populations have also been shown to be jeopardizing human reproductionAccordingly, animal studies on endocrine disrupting properties of toxic chemicals are relevant to understanding human responses to these chemicals. Pesticide mixtures have been shown to be powerful endocrine disruptors in numerous other animal studiesJ16 Illustrative examples follow. 

A large number of individual chemicals have been demonstrated to be endocrine disruptors. EDCs include pesticides, synthetic hormones, heavy metals, plasticizers, and other industrial chemicals. Table 22.1... 

Sperm counts in men have declined by about 50% during the time period 1940-90, from an average of 113 million per milliliter of semen in 1940 to an average of 66 million in 1990. During the same time frame there has been a decrease in seminal volume from 3.40 to 2.75 ml. 51 The reasons for the observed decline in semen quality are exposures to pesticide mixtures 52 and other xenobiotic endocrine disruptors, 53 maternal consumption of beef-containing anabolic steroids 54 and other xenobiotics, and tobacco smoking. 55 ... 

As an historical note, the book Our Stolen Future by Theo Colburn was published in 1996 and launched much of the controversy surrounding the topic of endocrine disruptors. It has been compared to Silent Spring by Rachel Carson, published in 1962, a book about pesticide use that is widely credited for starting the environmental movement in the United States. ... 

Herbicidal 2,4-D selectively kills broadleaf weeds and is the most widely used of all herbicides worldwide on wheat, corn, rice, and other cereal grass crops. It is a synthetic auxin, or plant hormone that is absorbed through leaves, is transferred throughout the plant, and causes unsustainable growth that results in plant death. Fortunately, given its widespread use and human exposure, it has very low acute toxicity. It is possibly carcinogenic, a status shared with many other pesticides, and is a suspected endocrine disruptor (see Chapter 2, Section 2.16). 

Contamination of the environment and agricultural products with endocrine disruptors(EDs) including dioxins, industrial chemicals and certain pesticide residues is a serious problem. These chemicals were found in the environment and agricultural products at nano-level concentrations, and are suspected of affecting ecosystems and human health. The Ministry of the Environment of Japan surveyed contamination of EDs in rivers, showing that bisphenol A, 176-estradiol and nonylphenol were detected in 50.3%, 40.4% and 31.0% of the water samples, respectively(Table 1). 

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