Extremophile Hotspots Linked To Containerized Industrial Waste Dumping In A Deep-sea Basin

Editor’s note: Over the past several decades our definition of “life as we know it” on Earth has undergone a paradigm shift as we have discovered various “extremophiles” living in environments that orthodox biology would see as being “extreme”. These extreme environments may be more normal and common – and important – than we once thought. The environments that extremophiles inhabit may resemble the environments wherein life first originated and evolved on Earth. Of course, evolution is still ongoing. The disposal of large amounts of toxic materials seems to have eliminated many life forms in the deepest reaches of the ocean while providing a novel albeit extreme environment. Organisms – perhaps nascent extremophiles already equipped with some adaptive traits can survive, adapt, and thrive. How these adaptations happen and morph during evolution will be instructive not ony in understanding life’s origin but also the range of locations on this world – and on others – where life (as we mostly understand it) can exist. Of course dumping these poisons into our oceans is not a smart idea in the first place.

Decaying barrels on the seafloor linked to DDT contamination have raised concerns about the public health implications of decades old industrial waste dumped off the coast of Los Angeles.

To explore their contents, we collected sediment cores perpendicular to five deep-sea barrels. The concentration of DDT and its breakdown products were highly elevated relative to control sites yet did not vary with distance from the barrels, suggesting that they were not associated with the contamination.

Sediment cores collected through white halos surrounding three barrels were enriched in calcite and had elevated pH. The associated microbial communities were low diversity and dominated by alkalophilic bacteria with metagenome-assembled genomes adapted to high pH.

Barrel sampling. Barrels without (A) and with a white halo (B) were sampled as shown. Sediment cores are depicted as gray columns divided into four 2-cm depth horizons. C) ROV recovering a sediment push core. D) Two barrels without white halos (1N and 2N) were sampled during dive S0450. E) Three barrels with white halos (1S–3S) were sampled during dive S0451 along with the concretion surrounding barrel 3S. — PNAS Nexus

A solid concretion sampled between a white halo and barrel was composed of brucite, a magnesium hydroxide mineral that forms at high pH. Based on these findings, we postulate that leakage of containerized alkaline waste triggered the formation of mineral concretions that are slowly dissolving and raising the pH of the surrounding sediment pore water.

This selects for taxa adapted to extreme alkalinity and drives the precipitation of “anthropogenic” carbonates forming white halos, which serve as a visual identifier of barrels that contained alkaline waste. Remarkably, containerized alkaline waste discarded >50 years ago represents a persistent pollutant creating localized mineral formations and microbial communities that resemble those observed at some hydrothermal systems.

These formations were observed at one-third of the visually identified barrels in the San Pedro Basin and have unforeseen, long-term consequences for benthic communities in the region.

Extremophile hotspots linked to containerized industrial waste dumping in a deep-sea basin, PNAS Nexus (open access)

Astrobiology, Microbiology, oceanography,