An important feature of the male testes is the lining of Sertoli and Leydig cells. They play a crucial role in the development of sperm. Prior to puberty the Sertoli cells are able to convert testosterone into the oestrogen. Exposure to oestrogens in the environment
has the potential to damage Sertoli and Leydig cells and their important function of masculinization and sperm development.

In adult women, exposure to abnormally high levels of oestrogen can affect the fertility of the ovaries and the efficiency of the oviduct. It can stimulate excessive growth of tissue in the uterus and in the breast leading to cancer.

Their effects may well be complex. Some chemicals have been shown to have anti-oestrogenic properties such as the dioxin TCDD and the bioflavanoids found widely in food..

NATURAL AND SYNTHETIC HORMONES

Apart from the pill, the best known example is that of DES which was administered to women to prevent miscarriages from the early 1950s until its use was stopped in the early 1970s. A significant number of female offspring developed problems with their reproductive organs, pregnancies and menstrual cycles. Male offspring developed symptoms which included cryptorchidism microphallus and decreased sperm count. DES has been used as a growth promoter in cattle exposing humans via meat products.

Evidence of environmental pollution by the large amounts of oestrogen excreted by pregnant women and female animals has been elusive.

PHYTOESTROGENS (plant derived)

These are compounds with oestrogenic activity found naturally in edible plants such as peas, beans, cabbage, sprouts, spinach, grains and hops. If consumed in large quantities there is evidence of significant biological effects. Some phytoestrogens also act as anti-oestrogens. Whilst there may be adverse effects from such substances in the diet it is probable that this is balanced by the benefits of a high plant food diet.

ORGANOCHLORINE PESTICIDES

Whilst the use of organochlorine compounds such as DDT, dieldrin, lindane, chlordecone
and others as pesticides has declined in the industrialised world over recent decades, their ability to accumulate and concentrate in biological systems remains a source of concern. Their residues can remain in human tissue for long periods. A recent study [9] has shown that one of the breakdown

products of DDT, known as p,p'-DDE, is an especially effective anti-androgen. Some studies have linked DDE with lactation failure in mothers and breast cancer.

POLYCHLORINATED BIPHENYLS

Despite decreasing use and bans on the production of PCBs, large quantities have been dispersed into the environment. Studies have indicated a number of ways in which PCBs can interfere with the human hormone system and may be linked to breast cancer. However, conclusive evidence has been difficult to achieve because of the large number of varieties (congeners) of PCBs and the probability that effects vary between each. Two major accidents involving PCBs in the Far East produced abortions and low birth weight in surviving children.

DIOXINS

This family of substances known as PCDDs (dioxins) and PCDFs (furans) are not commercial products but arise from incineration and as waste products from industry. Though the volume produced is very low the toxicity is extremely high. Human exposure is usually via food, especially meat, milk and fish. Dioxins have been shown to operate as anti-oestrogen and to have an adverse effect even at very low levels on the sexual behaviour and sperm production of rats. Another study has linked dioxins with endometriosis (abnormal growth of uterine tissue) in monkeys.

ALKYLPHENOL POLYETHOXYLATES (APES)

These are chemicals introduced into the UK in the 1940s and used extensively in cleaning
products, paints, herbicides and other industries. Whilst there has been special concern about the pollution of rivers from the discharges of these chemicals by industry because of their toxicity to aquatic life, human exposure also exists via other routes such as cosmetics.

Data on the potential health effects on humans is sparse; the main areas of concern arise from the possible intake via drinking water or by eating contaminated fish. APEs are known to have weak oestrogenic properties but may cause symptoms by working with other pollutants in the environment.

OTHER XENOESTROGENS

Herbicides atrazine and simazine: though neither of these chemicals has shown especially strong oestrogenic activity in studies, atrazine has been linked to breast cancer. Government studies have detected concentrations in sea water samples around the UK, the highest being around the Humber and Mersey estuaries.

Fungicide vinclozolin: Kelce [10] demonstrated that this chemical had effective anti-androgen properties on rats causing hypospadias, cleft phallus and other symptoms. It was concluded that similar effects could occur in the human fetus.

Phthalates: The phthalate DEHP is known to be toxic and to cause cancer in animals and may well be a hazard to humans because of its use as a plasticiser in medical and food packages and subsequent leaching out into the product [11]. Occupational exposure to high levels of phthalates has been shown to cause miscarriages in Russian workers [12].

RELATIVE LEVELS OF OESTROGEN INTAKE

The problem of assessing exposure to oestrogenic substances is compounded by the several factors such as the potential for accumulation and persistence versus the speed of degradation; the uptake of man-made chemicals in the environment has to be balanced against levels found naturally in foods or administered as drugs.