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On August 4th, an Environmental Protection Agency crew was working on a dam that was part of the old Gold King Mine in Colorado.  The workers were trying to fix the thing when suddenly, the dam broke, releasing more than 11 million liters of contaminated waste water into the nearby Animas River, turning it bright yellow.  This mine was one of thousands that opened in the 1870s at the start of the Colorado gold rush, and this one's been closed since 1923, with a whole lot of toxic waste just sitting there. 

At the time, mines often hit groundwater, which poured through the rock, reacting with sulfides to create sulfuric acid, and the big problem with sulfuric acid is that it's really good at binding with heavy metals that normally stay safely in the ground, like arsenic and lead, which you might recognize as things that you really do not want inside of your body very much.  We have a name for the resulting sludge that is created: acid mine drainage. 

The owners of the dam built the mine to contain all this stuff, but it hasn't held up very well over the last 92 years.  Before it broke, the dam was leaking about 750 liters of contaminated water per minute, and the EPA crew was sent in to stop it.  The workers were trying to install a pipe that would divert the water for treatment when they shifted some of the looser material and the dam burst.  A plume of contaminated waste water tinted yellow from iron containing compounds started making its way down the Animas River toward New Mexico.  Instead of the standard neutral 7 of pure water, the river's pH ranged from 3.74, roughly the acidity of tomato juice, to 4.58, the equivalent of black coffee. 

Communities along the river switched to other sources of drinking water and were advised not to use it for other things either, like kayaking or fishing.  Within a week, the EPA constructed two containment pools to treat the water that continued to pour from the mine, and the river's toxicity has already started to go down as the contaminated water is diluted.  All told, the drainage, despite its alarming color and toxicity levels, probably won't do too much long-term damage. 

According to the EPA, most of the wildlife should recover quickly, partly because the river's water was already pretty poor quality.  In the late 19th and early 20th centuries, mines dumped toxic waste directly into the river and for a while, nothing could live in it at all.  The water got a little better when the dumping stopped, but the organisms that have moved in are pretty resilient.  Still, there is concern about similar mines.  It's estimated that there are 55,000 in Colorado alone.  Many of them are slowly leaking the way Gold King was, and there's usually a few dams that burst every year, and as we've learned the hard way over the past couple of weeks, fixing them is another entry on a long list of tough scientific and engineering problems.

Meanwhile, researchers are working on solving another of those problems, namely, why do organisms reproduce sexually at all?  At first glance, asexual reproduction seems like a much better way to do things.  You can just create offspring whenever, no need to go around the messy business of finding a partner.  In a new study published this week in the journal Science, a group of American biologists may have found part of the answer in the fruit fly genome.  It's thought that one of the main benefits of sexual reproduction is greater genetic diversity, having partners means that offspring can have lots of different combinations of alleles of a various gene, and if you have a big diverse population, it's much more likely that a few of them will be resistant if there's a threat, like an outbreak of disease.  The researchers wanted to figure out if a threat can actively spur that evolution so they divided a group of female fruit flies into two and infected half of them with a parasite and then let all the fruit flies reproduce sexually.  Most fruit flies cells, like human cells, contain two copies of each chromosome.  When they produce eggs, pieces of DNA from both copies get combined into one set instead of two in a process known as genetic recombination. 

In the infected females, genetic recombination tended to happen a lot more, so they had very diverse baby flies . According to the researchers, it's possible that the threat of the parasite drove the infected flies to produce more diverse offspring, but there's still a lot we don't know.  For one thing, the team isn't sure exactly how the infected flies produced eggs with more shuffled genes.  Plus, just because this is true for fruit flies doesn't mean it happens in other species like humans, so there's still plenty of research to be done on the many reasons sex is a thing.

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