Hormone disruptors in ecosystems

In recent years effects on reproduction have been identified in a large number of animal species and these effects have been attributed to the influence on hormonal systems of certain substances that are present in the environment. The supposition has been expressed in various publications that such substances also have an impact on human beings. In 1997 the Health Council of the Netherlands reached the conclusion that this supposition has not been verified for the Dutch population. In this advisory report, the Health Council — acting upon the request of the Minister of Housing, Spatial Planning and the Environment (VROM) — describes the current level of knowledge on the effects of hormone disruptors on animal reproduction in Dutch ecosystems.

The Committee focuses primarily on substances that interfere with the sex-hormone hormone balance. It calls a given substance a hormone disruptor if it is capable of disturbing reproductive physiology. The Committee also considers the effects of substances on the thyroid balance, in view of the important role which this system plays in development and reproduction.

In order to chart the implications of hormone disruptors for the situation in the Netherlands, the Committee has conducted an inventory of the field research that has been carried out in this country. In addition, it has classified around 80 pesticides and substances of industrial origin according to their hormone-disrupting capacity in the Dutch environment. The presence and possible effects of a number of natural and synthetic hormones have also been surveyed. These substances are excreted in substantial quantities by humans and especially by livestock.

In contrast to the situation in humans, effects on animal reproduction have definitely either been demonstrated, or else they are likely, in Dutch ecosystems. The majority of studies relate to animals in aquatic ecosystems (including animals predating in these systems), with much less being known about the effects of these substances on animals that live on the land.

Intersexuality is prominent among the (possible) harmful effects that are associated with the presence of such substances in the water compartment. It is clear, for example, that certain species of snail which inhabit the coastal areas of the North Sea have, to some extent, been affected by a specific substance (tributyltin). It is not known what impact this has on populations of different species that are present in the food chain, and thus on the functioning of the ecosystem as a whole. Unfavourable phenomena have also been identified in fish, which are attributable to the impact of hormone disruptors. What remains unclear, however, is precisely which substances are involved and the scale of the effects in question. According to British research, there is a link between intersexuality, which has been discovered on a large scale in certain fish populations, and the occurrence of increased levels of a specific protein (vitellogenin) in male fish. Such increases point to an oestrogenic effect caused by substances that are present in the environment. Based on research in our country, although as yet limited, it also appears that an increase of vitellogenin in male fish is occurring in the Dutch estuaries.

According to the Committee, there is sufficient evidence of the negative effects of DDE, PCBs and dioxins on reproduction in certain species of fish-eating birds and (marine) mammals. These effects have — especially in the past — led to a decrease in (local) populations. The environmental concentrations of these substances — especially in sedimentation areas of the Rhine, Meuse and Scheldt rivers — are still so high that an adverse impact on the reproduction and development of resident fish-eating top predators can still be expected.

The Committee designates 34 of the 80 or so pesticides and substances of industrial origin in the Netherlands as (potential) hormone disruptors. These are alkylphenols, organochlorine, organobromine and organotin compounds, phthalates and triazines. Some of these substances — for example, the organochlorine compounds — have mainly been used in the past, while in other cases usage — and therefore dispersion in the environment — is more recent. Examples of the latter category are the persistent organobromine compounds, which have already penetrated deep into the food-chain in the oceans. For the majority of substances, data are only available about mammals. For these substances it is therefore impossible to verify the extent to which xenobiotic substances play a role in aquatic animals and invertebrates.

The Committee also regards some natural and synthetic oestrogens as hormone disruptors. These substances are excreted in substantial quantities by humans and, in particular, by livestock and find their way into the surface water by a process of leaching and via sewage treatment plants. The concentrations of these extremely potent hormones in the major rivers are, broadly speaking, sufficiently high to give rise to effects on aquatic animals. In this regard, the Committee points out that it is likely that even higher concentrations of natural hormones occur in surface waters in areas of intensive livestock production.

According to the Committee, there are sufficient scientifically founded grounds for concern over the presence of substances — especially in the aquatic environment — which are capable of disrupting the sex-hormone balance in organisms and which might therefore pose a threat to the continued existence of species in ecosystems. In some species, effects on individuals and populations have actually been demonstrated, or else they are likely. Precisely what implications this has for biotic communities and entire ecosystems is unknown. However, because only very limited research has been carried out into the effects of the hormone disruptors that are present in the environment, it is quite possible that hormone disruption is more widespread than appears from the present report. It is precisely because many substances have been investigated in recent years for their hormone-disrupting action that this list has already grown considerably. Given the large quantity of substances that stand to be investigated over the next few years, it is reasonable to suppose that the number of substances that can be labelled as (potential) hormone disruptors will continue to rise substantially.

In this connection it should also be borne in mind that the Netherlands occupies a unique position in Europe as far as the presence of hormone disruptors in the environment is concerned. Various European rivers bring hormone disruptors into the Netherlands. Because the Netherlands is a sedimentation area, it is precisely the persistent hormone disruptors that remain in the sediments. This country also has an extremely intensive agriculture industry which uses various substances that (possibly) exhibit hormone disruptive effects. Account also needs to be taken of the presence in this small country of natural hormones as a result of its large numbers of humans and, in particular, livestock.

The Committee recommends that the monitoring programmes should be focused primarily on the water compartment and on manure. As far as the natural hormones are concerned, maximum priority needs to be given to small ditches and manure. Of the other substances, attention needs to be focused principally on the 34 substances which the Committee has classified as (potential) hormone disruptors, with the exception of a number of the organochlorine compounds, for which a successful policy has already been implemented. In view of its conclusion that little field research has been conducted into the effects of hormone disruptors within ecosystems, the Committee advocates that those monitoring programmes that already exist should be extended.

The Committee concludes that the instruments that are already available for monitoring effects on the sex-hormone balance in animals — although limited — are, nevertheless, adequate. These instruments include, amongst others, age structure and sex ratios of populations, transplanted sentinels, in vitro tests and chemical monitoring. It recommends extending the existing monitoring programmes with some of these techniques. The Committee emphasises the fact that there is no proven approach and that monitoring requires an iterative process, involving interdisciplinary collaboration, whereby ongoing efforts are made to determine which approach is the most effective.