Wastewater from Alberta's oil sands inhibits fish reproduction.

Kavanagh, RJ, RA Frank, KD Oakes, MR Servos, RF Young, PM Fedorak, MD MacKinnon, KR Solomon, DG Dixon and G Van Der Kraak. 2010. Fathead minnow (Pimephales promelas) reproduction is impaired in aged oil sands process-affected waters. Aquatic Toxicology http://dx.doi.org/10.1016/j.aquatox.2010.09.021.

While water from oil sands mining reclamation pits is not overtly toxic to fish – it does not kill them outright – it can inhibit their reproduction enough to limit the fish population over time, finds a Canadian study.

After sitting in pits for 15 years, mining wastewater from four out of five ponds sampled in Alberta's oil sands area inhibited egg production, decreased male sex characteristics that develop during puberty and skewed hormone levels in adult fathead minnows exposed to the wastewater under laboratory conditions. 

The results show that more concerted effort – and not just time – may be needed to clean up the wastewater produced during mining of the oil sands. One of the tested pits that did not significantly impair fathead minnow reproduction may offer clues about how best to clean and naturalize mining wastewater.

Oil sands mines in Alberta provide more than 40 percent of Canada’s oil production. The ore from the oil sands contains a mix of sand, clay, water and bitumen – heavy, biodegraded crude oil. During mining, the bitumen is separated from the sand and clay in a process that yields large amounts of wastewater. The wastewater is heavily contaminated with tiny suspended particles called mature fine tailings (MFT) and a mix of chemicals called naphthenic acids (NA), which occur naturally in unrefined crude oils. They are known to affect fish physiology and reproduction.

This wastewater is held in large ponds where the MFT and other particulates settle out. The water can then be reclaimed and reused for additional mining activities until the mine shuts down.

However, the basins remain even when a mine no longer operates. The enormous polluted pools have high concentrations of MFT.  Currently, Alberta has more than 1 billion cubic meters – equivalent to about 264 billion U.S. gallons – of mining-affected, MFT-contaminated wastewater that must be cleaned up and returned to the environment.

The current reclamation option is to transfer the wastewater to nonporous pits where the toxicity is expected to decrease with time, encouraging the natural development of lake habitats.

To help determine if this expectation is realistic, researchers exposed adult fathead minnows to either mining wastewater that was aged for at least 15 years and sampled from five pits managed by oil sands companies in Alberta or water from a nearby natural lake. The laboratory exposures lasted 21 days.  The researchers monitored the number of eggs spawned, egg fertilization rates, hatching rates and 96-hour survival of offspring. Organ weights, blood hormone levels and the number of male head bumps – called tubercles – were also measured.  Tubercles grow on the heads of male minnows when they reach reproductive age – a similar, hormone-driven characteristic as a man's beard. 

Fathead minnows are native to Alberta and would be expected to inhabit ponds created from mining waste-water. They are also widely used for exposure research, so their reproduction is well understood.

None of the exposed fish died, but the wastewater affected their ability to reproduce. The exposures lowered egg production, significantly altered male sexual characteristics and decreased blood levels of important reproductive hormones – testosterone, 11-ketotestosterone and 17ß-estradiol – the main estrogen – when compared to the fish exposed to lake water. The altered hormones are the most likely cause of the other reproductive problems, the authors suggest.

But, as the ranges show, the changes were not uniform across all pits. For example, the number of eggs produced declined from 10 to 75 percent compared to control fish.  Changes in hormone levels ranged from no change to a decrease of 70 percent, depending on the hormone. Tubercle number dropped up to 60 percent.

The most drastic effects were seen in fish exposed to water with high levels of naphthenic acids and minerals that contribute to "hard" water – such as, sodium, sulfates and carbonates. These contaminants are commonly associated with oil refining.