How many drips does it take to make a splash?

In late April of 2010, the Deepwater Horizon oil rig in the Gulf of Mexico had a catastrophic failure. For the better part of three months, images of oil slicks, outraged politicians and environmental groups decrying the damage being done dominated our news media before the ongoing spill was stopped and the coverage trailed off. Estimates of the amount of oil released during the incident are officially 4.9 million barrels and could have reached as high as 5.4 million barrels. (753 000 to 830 000 tonnes)

Fortunately, spills of this size are rare, and the previous largest North American spills on record were from 22 years earlier when the tanker Odyssey went down off of Nova Scotia (Canada) in 1988 and the smaller but well-reported Exxon Valdez spill off Alaska (USA) in 1989. Combined, these three events released approximately 925 000 tonnes of oil into the marine environment.

Based on previous reports by the US-based National Academy of Sciences, it is estimated that 84 000 tonnes of oil products are released in North America through on-land human activity each year and enter the marine environment through run-off and other means, mainly through storm and sewer drains.

This means that in the 22 years that the big spills cover, our on-land spills dripping from old cars, leaky equipment and general carelessness would have totalled 1 848 000 tonnes or about double what the highly publicized offshore spills generated.

With the coverage given to the off-shore spills, how many breaking news stories have you seen about the amounts of oil spilled by the average member of Joe Public? How many drips will take to make a splash?