A recent Harvard University study concluded that avoiding a toxic worker was worth about $12,500 in turnover costs.

Keeping unsafe workers from spreading their cancer will not only save a company money, it improves productivity. Your high performers will especially thank you.

Here are some telltale signs of toxic worker behavior which could send your best people packing.

They gossip.

You know who they are--most likely disgruntled workers who didn't get something their way, disagreed with a change of direction and are now holding grudges, or didn't get that promotion they felt entitled to.

They are quick to gossip, and even quicker to hammer leadership for "dumb decisions."

Keep a close eye on them. They spread their tumor by enlisting others into their negative spin campaign. They'll also be sure to befriend those innocent new hires to vilify someone or something.

They are not accountable.

When self-awareness is present accountability blooms. Not so with these toxic workers. They don't exercise responsibility and own up to "their stuff" when "their stuff" is at fault. Remember the old saying, "For every finger you point, there's three pointing back at you"?

They create roadblocks to disrupt your work.

You may shake your head in agreement because you've seen it and it still astonishes you! They will go way out of their way to sabotage anything you're trying to get done. So you're left with covering your basis to protect yourself -- writing more detailed emails than usual, CCing and BCCing more people than normal, and making backup copies of everything in the event a false accusation comes your way.

They intimidate.

35 percent of U.S. workers report being bullied at work, according to a 2010 Workplace Bullying Institute survey. Interestingly enough, women bullies target other women in 80 percent of the cases. It can devastate careers and ruin your health.

Babs Ryan, author of America's Corporate Brain Drain, says, "Only 1 percent of bullies are fired; action is usually taken against the [bully's] target. Your only choice may be to leave as quickly as possible -- especially if the company supports that bully repeatedly and has already exited several of the bully's targets."

They kiss up to management to win favors, at your expense.

They will go out of their way to befriend and manipulate management in order to negotiate preferential treatment--undue pay raises, training, time off, or special perks that nobody else knows about or gets. Keep an eye out for colleagues that spend way more face time with their managers than usual. The wheels of favoritism may be in motion.

They are two-faced.

Their dirty work involves lifting you up and saying how great you are to your face, and later spreading lies and rumors to someone else about what a lousy employee you are. They cannot be trusted as far as you can throw them.

Now what? What do you do?

First and foremost, steer clear and don't get sucked into the toxicity. If you work in a small startup with no HR function, and you love your job and see long-term potential in the company, the bravest thing to do is nip this problem in the bud pronto! Expose the problem, talk about it with those you trust, and campaign against it with your closest allies.

In larger companies, report such behaviors to your HR team. But--and this is a BIG but--if your management has the backs of your toxic workers, they are--themselves--toxic workers. It's just not worth it to put up a fight at this point. Be ready to leave with a backup plan in place.

Have you worked with toxic co-workers? What would you add to this list?