Pollutants in the sea - a threat to dolphin and porpoise populations?
A major European project on contaminant levels in marine mammals has discovered high levels of chemicals known to affect reproductive rates in harbour porpoises from Dutch waters and along the coasts of North West Scotland and Ireland, and in common dolphins from the English Channel.
The three-year study aimed to quantify levels of persistent organic pollutants (POPs) and heavy metals in harbour porpoises and common dolphins in different parts of the NE Atlantic. Certain organic pollutants, eg polychlorinated biphenyls (PCBs) are known to depress reproductive performance and the immune system. They are also known as "hormone disruptors" and have a particular affinity for fat, which means that they accumulate in the blubber of dolphins and porpoises.
Highest levels of PCBs were found in harbour porpoises from Dutch waters and common dolphins from the English Channel. These levels were high enough to have an impact on reproduction. Evidence collected on pregnancy rates suggests that the reproductive rate in Dutch porpoises is considerably lower than recorded elsewhere in Europe. Although this fits with the results on PCB levels, Dutch porpoises also carry
the Brucella bacterium. Although its effects in cetaceans are unknown, in cattle it can cause the first pregnancy to end in abortion. This bacterium is also present in other porpoise populations, including that in Scotland.
Dr Graham Pierce, Senior Lecturer, University of Aberdeen, co-ordinated the project. He said: "Our most interesting new results have to do with the occurrence of brominated flame retardants (BFRs) in porpoises.
One of these compounds is hexabromocyclo-dodecane or HBCD, which has a high production volume -9500 tons was produced within the EU in 2001. BFRs are used in the building industry."
Dr Pierce added: "Highest HBCD levels occurred in harbour porpoises stranded on the coasts of the Irish Sea and on the North West coast of Scotland.
"Much less is known about these chemicals than about PCBs but they could have similar adverse effects on the immune system and reproduction. These measurements of BFRs were made by colleagues from the Royal Netherlands Institute of Sea Research. They are now working on another project to look at possible effects of these compounds."
Research groups from Scotland, Ireland, France, the Netherlands and Spain were involved in the study which has been submitted to the European Commission's Energy, Environment and Sustainable Development programme. The work was based on analysis of samples from animals found dead on the coast, and also looked at the possible causes and consequences of the pollutant levels that were recorded. In Scotland, the project worked closely with the UK government's cetacean strandings project, under which Scottish Agricultural College Veterinary Services Division provided all the Scottish samples.
MORE BACKGROUND:
Small cetaceans - such as common dolphins and porpoises - face a number of threats in European waters which include incidental catches in fishing gear, depletion of prey resources, habitat degradation, disturbance by ship traffic and coastal development. Accumulation of these organic pollutants adds to the pressure on their populations.
Of more recent concern are the brominated flame retardants with chemical structures closely resembling those of the PCBs which means they are also "potential hormone disruptors"
The BIOCET project set out to try to quantify the accumulation of persistent organic pollutants (POPs); the "classical" organohalogen compounds and the relatively new PBDEs on the reproductive success of selected populations or harbour porpoises and common dolphins in relatively unpolluted and highly polluted areas within European Atlantic waters.
The project looked at Irish, Scottish (UK) and Dutch coasts, as well as the Atlantic coasts of France and Spain. Of these areas, Dutch waters, in particular, are considered to be "highly polluted".
The study involved female harbour porpoises and female common, striped and bottlenose dolphins which were found stranded in Scotland, Holland, Ireland, France and Spain. Various samples including teeth, ovaries, blubber and stomach contents were analysed.
Researchers found that PCB concentrations in the blubber are higher in porpoises from the Netherlands than in those from Scotland and Ireland and this corresponds to a much lower estimated pregnancy rate in the Dutch porpoises.
Data also indicated that PCB levels were higher in males than in females, and that levels started to decline in females after maturity is reached. These differences are well known and arise because substantial amounts are transferred to the offspring in the mother's milk, which is very rich in fat.
The study found that of all the pollutants, PCBs were the most likely to have an impact on reproduction - the highest levels (in porpoises from the Netherlands) corresponded to the lowest pregnancy rate recorded for harbour porpoises.
However researchers point out that there was a relatively high incidence of Brucella in Dutch harbour porpoises, which could also contribute to the low pregnancy rate. Adult female porpoises normally breed once every 2 years in European waters, but the figure could be as low as once in 10 years for Dutch porpoises. We cannot be sure exactly how Brucella affects cetaceans but in cattle it is only the first pregnancy that ends in abortion.
The highest HBCD (hexabromocyclododecane - a brominated flame retardant) levels were found in harbour porpoises stranded on the coasts of the Irish Sea and the NW coast of Scotland. The effects of BFRs are not so well known, as they are relatively recent chemicals. However these chemicals are similar in chemical structure to other compounds that are known to affect reproduction rate, so there is cause for concern.
The dolphins and porpoises are taking in these chemicals in their food, mainly fish. These chemicals occur throughout our environment, in the sea and on land. Because chemicals like PCBs have an affinity for fats, dolphins are prone to accumulate them in their blubber layer. There is less danger for humans in that we do not have the same capacity to "bioaccumulate" these chemicals - although it is known that, in human societies where whales or seals are eaten, people can build up very high levels of PCBs in their bodies.
The project involved the following teams of researchers:
University of Aberdeen: Dr Graham Pierce, Dr M. Begoña Santos, Ms Jennifer Learmonth
University College Cork (National University of Ireland): Dr Emer Rogan, Ms Sinead Murphy
National Museum of Natural History, Leiden, Netherlands: Dr Chris Smeenk and colleagues
Royal Netherlands Institute of Sea Research: Dr Jan Boon, Dr Bart Zegers and colleagues
Laboratoire de Biologie et Environment Marins, Université de la Rochelle: Dr Vincent Ridoux, Dr Florence Caurant and colleagues
Instituto de Investigaciones Marinas, Consejo Superior de Investigaciones Científicas: Dr Angel Guerra and colleagues
Centre de Recherche sur les Mammifères Marins, La Rochelle, France: Mr Olivier van Canneyt, Mr Willy Dabin and colleagues
Our main collaborators were:
The UK strandings project, led by Dr Paul Jepson (Institute of Zoology, London) and also involving Mr Tony Patterson and Mr Bob Reid (Wildlife Unit, Scottish Agricultural College Veterinary Services), and Dr Robin Law (CEFAS)
The Marine Laboratory Aberdeen: Dr Colin Moffat
The University of Liege, Belgium: Dr Jean-Marie Bouquegnau and Dr Thierry Jauniaux
The University of Brussels: Dr Claude Joiris, Dr Ludo Holsbeek
Age Dynamics, Denmark: Dr Christina Lockyer
CEMMA, Galicia, Spain: Dr Alfredo Lopez, Mr Josep Alonso and colleagues