It's no secret that the world's oceans are in a pretty bad way, with David Attenborough recently saying that they are currently under the 'biggest threat in human history'.
"For years we thought the oceans were so vast and the inhabitants so infinitely numerous that nothing we could do could have an effect upon them. But now we know that was wrong," Attenborough said in the final episode of Blue Planet II.
"It is now clear our actions are having a significant impact on the world's oceans. [They] are under threat now as never before in human history. Many people believe the oceans have reached a crisis point."
However, while we mostly think of ocean pollution as mounds of plastic bottles, straws and six pack rings, it turns out there's one thing that many of us have forgotten about: cigarettes.
Yep, according to data collected by NGO Ocean Conservancy, around 60 million cigarette filters have been collected since the 1980s, making them the single biggest source of ocean pollution.
In fact, there are so many of them that in the past year 2,412,151 cigarette butts have been collected - enough to line the distance of five marathons.
Far exceeding the numbers of plastic bags, food wrappers, straws and drinks bottles that have been found in the sea, cigarette filters can cause irreversible damage to both wildlife and the ocean itself.
According to Business Insider, most cigarette filters aren't actually biodegradable, as many assume. While many filters contain cellulose acetate, which is itself a natural product, there is also a non-biodegradable plastic that forms when the cellulose acetate is processed - meaning that it actually takes way longer for a cigarette filter to break down than people think.
The filters also release all the pollutants that they've absorbed from the smoke - we're talking substances like nicotine, arsenic and lead, all of which get consumed by sea creatures. Sometimes these then end up appearing in our own food again, too.
Of course, it's not always a case of people throwing their butts directly into the sea, or stubbing them out in the sand while at the beach. Sometimes it's simply a case of butts being carried by the rain into rivers, before eventually reaching the sea.
The cigarette industry is looking at alternatives for the production of filters, but realistically, you're best of looking into disposing of butts responsibly - or, of course, not smoking.
Featured Image Credit: PA