Wildlife are exposed to a cocktail of hormone-disrupting toxins and our understanding of the risks is limited

27 February 2019

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Wildlife are exposed to “complex cocktails” of pollutants that could disrupt their hormones and affect growth, development, reproduction and health. An expert review on endocrine-disrupting chemicals (EDCs) from the Oxford Martin School at the University of Oxford concludes today that although much is known about individual chemicals’ impacts, scientists’ understanding about the effect of this mixture of compounds is limited. This lack of an evidence base is a challenge for policymakers, particularly in light of the growing presence of different EDCs in our river and ocean environments.

A team of experts convened by Professor Sir Charles Godfray of the Oxford Martin School has assessed the evidence base of key chemicals known to disrupt the endocrine system of wildlife, in order to better inform policy decisions, provide clarity on the broad scientific consensus, and show where crucial knowledge gaps lie. This restatement, published today in Proceedings of the Royal Society B, is the latest in an ongoing series, consisting of policy-neutral reviews of the science evidence base in areas of concern and controversy.

The endocrine system is the collection of glands that produce hormones. It plays a critical role in almost all biological and physiological functions including growth, organ function and reproduction. Synthetic endocrine disrupting chemicals come from a variety of products including many plastic goods, human and veterinary pharmaceuticals, flame-retardants and manufacturing chemicals. They can leach from the plastic in poorly managed landfills, be contained in agricultural run-off, and be discharged into rivers and oceans as part of treated or untreated wastewater.

Treated domestic wastewater can contain natural oestrogens as well as synthetic oestrogen and progestin used in contraception, hormone replacement therapy and cancer treatment, anti-depressants like fluoxetine, and metformin - a drug used to control blood sugar in patients with Type II diabetes. Of over 140,000 compounds registered under the EU’s Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) the number found to or suspected to have endocrine disrupting properties of various potencies is 800-1,000.

“The EU’s REACH legislation was designed to help fill the large gap in toxicity knowledge that there is presently,” commented Professor John Sumpter, Professor in Ecotoxicology, Brunel University London, “but we are presently a very long way from understanding based on a chemical’s structure alone if it will cause adverse effects in the environment, on what species, and at what concentration. Getting this toxicity information using current processes is very time consuming and expensive.

“Of the EDCs we understand and know are being released into wildlife habitats, the EDCs derived from plastics and electronic waste are of particular concern. However, the presence of EDCs in many further products is unknown, as labelling has not been required. Because of this, much material containing EDCs continues to end up in landfill, in particular PCBs and flame-retardants, despite regulations intended to control their disposal.”

Polychlorinated biphenyls (PCBs) are highly toxic and bio-accumulative (fat soluble) chemicals and have been subject to global bans since 2004. They are very long-lasting in the environment. In the UK there is an orca (killer whale) population in Northwest Scotland with high PCB exposure and toxicity in which no calves have been observed in 25 years. A recent predictive model suggests 40-50% of orca populations globally could face extinction within 100 years because of PCBs, mainly due to their very high rates of maternal transfer and associated toxicity to calves (both in utero and via milk).

Dr Paul Jepson, European Veterinary Specialist in Wildlife Population Health at ZSL’s (Zoological Society of London) Institute of Zoology said, “The potential threat to wildlife from EDCs became widely accepted in the 1960s-1980s and since then we’ve seen national or international bans on some harmful substances. However, in almost all cases when an EDC has caused adverse effects on wildlife the connection has only been established after the wildlife population had declined.”

Despite the large number of EDCs present in the environment, particularly accumulating in aquatic ecosystems, studies generally look at the effect of an individual EDC on a single species or locality. There is evidence that EDCs with similar endocrine action combine additively and that opposing compounds may counteract each other. Yet, overall knowledge of how EDCs interact with each other and other pollutants is limited.

Sumpter continued, “EDC release into the environment will be affected by economic and demographic trends. Increased plastic consumption, the rise in anti-depressant use and diagnoses of Type II diabetes, and the release of deposited EDCs from melting Arctic ice will all increase the environmental presence of EDCs. Yet, substantial uncertainty exists about the potential negative environmental impacts of EDCs, and the extent to which their toxicity can be predicted before introduction is limited. Policy-makers need to balance the known risks outlined in this restatement and the known unknowns identified with the economic, health and other benefits of each substance.”