California

Some good news:

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 {the barrels} were not associated with the contamination.

Other good news, it appears, is that if there is a huge proportion of alkali in those barrels, there's that much less DDT etc. simply for lack of room. Again, the long-term danger represented by the alkali is minimal -- in fact, seawater around the globe is increasing in acidity, so these may abate that by a quadrillionth part or so.

The latter included steel barrels that were reportedly punctured to facilitate sinking (1).

This would have allowed water and dissolved alkali to move in and out slowly & diffuse outward, and would have dissipated the alkali over time. Apparently, they didn't hole all of the barrels, or maybe this was due to some variation in contents.

It appears the DDT contamination may be a vestige of earlier mass dumping into sewers:

Montrose legally discharged thousands of gallons of DDT-contaminated acid and alkaline waste into the Los Angeles municipal sewer system, which heavily contaminated the Palos Verdes Shelf (1). Waste disposal was extended to offshore sites, with barges used to transport both bulk and containerized waste.

The bad news here is that the DDT etc. is probably already all loose in that area, and removing the barrels, even intact, probably wouldn't abate that problem.

I'm a bit bothered by this quote from a postdoc associated with this study, who really should have known better:

“It makes you wonder: What was worse than DDT acid waste to deserve being put into barrels?”

It wasn't necessarily "worse" by any measure -- acid rapidly corrodes steel, so disposing of the acid waste in barrels was not an option -- as the report says, it was dumped into the sewer. BTW, acid waste is likely to be all, or mostly, liquid. Solid alkali can be safely stored in steel, but not aluminum containers, and dumping it down the sewer would have required a huge amount of water and would have evolved a tremendous amount of heat (handling solid or highly concentrated alkalis is, in many ways, more hazardous than handling most acids, but most people don't realize this). So disposal in steel drums was, most likely the "most practical" option -- i.e., cheapest in direct cost$, and we know how much that counts -- not a matter of what it "deserve{d}". But best of all, it may have just been NaOH or KOH pellets shipped in steel barrels -- the normal way -- which just proved to be excess inventory, and may have even been disposed of in unopened containers. If true, the possibility of other contaminants, including DDT etc., effectively vanishes.

Will post some final commentary after a short break