A quarter of a century after the Exxon Valdez  ran aground it is apparent that the Gulf of Alaska ecosystem is permanently damaged. Oil is still visible on the beaches and persists beneath rocks and sand where it is slow to decay.

A quarter of a century after the Exxon Valdez ran aground it is apparent that the Gulf of Alaska ecosystem is permanently damaged. Oil is still visible on the beaches and persists beneath rocks and sand where it is slow to decay.

March 24 marked the 25th anniversary of the environmental disaster caused when the Exxon Valdez tanker ran aground in the pristine waters of Prince William Sound in the Gulf of Alaska, dumping 35,000 tonnes of crude oil and fouling about 1900 kilometres of coast line.

A quarter of a century later it is apparent that the Gulf of Alaska ecosystem is permanently damaged. Oil is still visible on the beaches and persists beneath rocks and sand where it is slow to decay. Sea otter populations in the area are finally recovering, but many species are still listed as "not recovering". A pod of orcas that lost 15 of its 22 members after the spill has not produced a calf since. Pacific herring, once the source of a vibrant commercial industry and food for bald eagles, brown bears, seals, humpback whales and puffins, are also on this list.

The April 2010 BP Deepwater Horizon spill was the largest in US history, involving up to 600,000 tonnes of oil, so its likely impact will be larger and last longer. A study sponsored by the US National Oceanographic and Atmospheric Administration highlights the damage and the grim implications for the yellowfin and bluefin tuna and amberjack in the Gulf of Mexico. Researchers found a variety of heart abnormalities among fish exposed to low levels of crude-oil chemicals. Given the spill occurred during the tuna spawning season, those fish that were then embryos, larvae or juveniles have likely developed heart defects due to exposure to chemical toxins.

These fish, still several years from maturity, will be increasingly unable to catch food and will gradually be lost from the adult spawning population.

As in Alaska, the oil lingers in the gulf on the ocean floor and in the wetlands. The full extent of its impact will not be seen for many years. But studies show sick dolphin populations, sea turtles stranding at five times normal rates, decreasing fish populations and an unbalanced food web.

More worrying and less obvious are the potential effects on human health. There have been shockingly few studies done on the human health impacts of major oil spills. Exxon has consistently maintained there is no evidence workers in Alaska experienced any adverse health effects as a result of the clean-up, but in fact neither Exxon nor the US government has done any long-term research - a fact that only emerged at the time of the gulf oil spill. Now most of those itinerant or imported workers are lost to follow-up.

People living in gulf coast communities have reported a suite of illnesses involving headaches, nausea, respiratory problems and skin lesions. But the damage is likely to be more significant. Clinical investigations of more than 170,000 people who worked in some capacity to clean up the 2010 disaster show they have significantly increased risks of developing liver cancer, leukaemia and blood disorders. Some researchers are predicting increased rates of early-term miscarriages and cancers, along with liver, kidney and nervous system damage.

If these issues seem remote in Australia, that is only because the nation has escaped such environmental crises to date, but the potential for devastating oil spills sits just off the coast. The 2009 spill from the Montara Wellhead Platform, which lasted from August to November, was located 260 kilometres offshore in the Timor Sea and apparently caused little damage. However, given the spill involved conservatively 3600 tonnes of oil and 200,000 litres of dispersant were used in the clean-up, reassurances about long-term environmental impacts may be premature as much of that oil is still in the environment.

Meanwhile, BP is planning to drill in the Great Australian Bight, BHP Billiton wants to explore for oil near Ningaloo, off the north-west of Western Australia, and Woodside, in co-operation with Shell, has formally lodged plans to drill near Rowley Shoal, west of Broome. These are all environmentally sensitive areas. About one third of the total southern right whales in Australian coastal waters have been born in the sandy bays of the bight; Ningaloo is home to endangered sea turtles, and whales and dolphins swim around Rowley Shoal.

Environmental protection of these sites is made more precarious because Prime Minister Tony Abbott has followed through on his pre-election threat to Australia's national network of marine parks by suspending the management plans for 33 new marine parks, including parks in the Coral Sea, the Kimberley and the Great Australia Bight.

The marine environment is already under serious threat. Offshore oil drilling adds to that threat, especially when the government favours less rather than more environmental protections.

Dr Lesley Russell is a research associate at the Menzies Centre for Health Policy, University of Sydney.