How Polyquat Works?

[jda]

In light of the recent concern with Vibrant containing polyquat and a massive usage, it might be a good idea to discuss how it works.

I have studied this pretty hard and asked some experts, even though very little about saltwater and nothing about aquariums seems to exist beyond anecdotes. I am not positive that any of this is correct, but I will lay it out as a starting point and we can edit it later.

What seems to be...

1. It has different results in freshwater than in saltwater, but lets focus on saltwater
2. Polyquat is a strong flocculant - it can make water clear
3. It will bind to any negatively charged surface seemingly indiscriminately - most live tissue is negatively charged and perhaps even rock and sand
4. It will stay bound until either absorbed into the organic tissue or perhaps just stay bound forever, or at least quite a while - polyquat is very stable
5. Water column will be free of the polyquat quickly, but it will be in the aquarium still bound to who-knows-what
6. Does not target algae over any other organic compound

What makes it so hard to figure out...

1. Seems to have different/faster effect on newer tanks with less diversity - seemingly less bio material for it to be bound to outside of the desired algae
2. Reported to have effects long after dosing
3. If bound to something in the water column, might be skimmed out or removed by GAC or other media
4. With the amount of organic material, rock and sand varying from tank to tank, this is why results (both good and bad) have such a wide range of dosages and time required for things to work

Let's add and subtract from this to get a baseline to help folks who currently use Polyquat, or might want to in the future.

Some past discussion:

Polyquat Stability in Reef Tank

Does anybody have any idea how long polyquat, or other QACs, would stay stable in saltwater after dosing them? Hours, days, weeks? Also, do they seem likely to be bound to GAC or get skimmed out thus diminishing their effectiveness over time? Thanks in advance.

www.reef2reef.com

 

[jeffww]

I think a lot about stuff like this (I work with colloidal systems and plants) and can probably write a good essay on this but firstly I think its a complicated topic. I think anyone who has done work in surface chemistry or membrane chemistry and colloids would agree. In this discussion it would be important to define what scales we are using to due theory. The bulk ion concentration is very different than the local experience of polymers and membranes. Also algae are cellular and work hard to maintain the local environment around the cell wall: the apoplast and conclusions made using bulk concentrations and ph may be invalid in the physiologically relevant length scale near the membrane within the apoplast.

 

[Doctorgori]

…probably germane thread about now, eitherway @jda how does vindication taste?

 

[jda]

I have been reading some more about this stuff and effect in water. Most of what is out there is for freshwater.

This stuff kills mollusks in saltwater like it is it's job. I would not even consider this if you have many clams.

It seems that once you dose, all of it could be bound up in literal seconds upon introduction.

Why do some corals get spared and some don't? This again is probably due to how fast the stuff binds and the indiscriminate nature of what it binds to. In tanks with more organic tissue and diverse lifeforms, any dose is probably quickly bound to waterborne organics, bacteria and micro fauna and never make it to the zoox. The host tissue would act as a shield, of sorts. Dosing size, amount of organic material would vary vastly.

It does appear to break down after quite some time. There are no actual studies or comments on this specifically for saltwater, but I would not be shocked if they compound stayed stable for a year or at least many months.

In the end, once you put it in your tank, you have no idea what it will bind to, no idea if any got filtered out, no idea what did not get filtered out and no idea how long it will last in the tank. If it happens to find algae and kill it, it was more of a random cooincidence that it hit some algae instead of some bacteria, a coral, fish, pod, or anything else.

If anybody else has any idea what to add to this, please feel free... just clearing up one or two unknowns might help a lot. Even educated guesses and theory are better than what we have now.

 

[Ghost25]

QACs are broad spectrum biocides, they can kill bacteria, fungi, cyanobacteria, and eukaryotic algae. The mechanism of action is disrupting cell membrane integrity.

QACs are surfactants, like soaps they have a polar (water soluble end) and a long nonpolar hydrocarbon tail (water insoluble). Designations like C18 refer to the number of carbons in the nonpolar tail.

Similarly cell membranes are composed of phospholipids which have polar and nonpolar ends. In the cell membrane these phospholipids form a bilayer with the nonpolar tails of two phospholipids adjacent and the polar heads at opposite ends to form a sandwich with a polar outside and nonpolar inside. This membrane is impermeable to polar molecules such as ions. The cell maintains a carefully controlled internal environment by regulating transmembrane traffic through tightly controlled protein gates such as pores and channels.

QACs integrate into the cell membrane and disrupt it's structure causing it to break apart and become permeable resulting in uncontrolled flow of molecules across the membrane.

QACs do exhibit specificity, at least in part to due the length of their nonpolar tails.

Selectivity of QACs to cyanobacteria

In aquatic environments QACs have a fairly short half life (0.5 to 2 days). Biodegradation is the most common route, not surprising as many QACs are naturally occurring, so many organisms have metabolic pathways to degrade them.

QAC aquatic environmental half life

 

[jda]

I think a lot about stuff like this (I work with colloidal systems and plants) and can probably write a good essay on this but firstly I think its a complicated topic. I think anyone who has done work in surface chemistry or membrane chemistry and colloids would agree. In this discussion it would be important to define what scales we are using to due theory. The bulk ion concentration is very different than the local experience of polymers and membranes. Also algae are cellular and work hard to maintain the local environment around the cell wall: the apoplast and conclusions made using bulk concentrations and ph may be invalid in the physiologically relevant length scale near the membrane within the apoplast.

How would somebody neutralize this stuff if they want to throw their bottle away safely?

 

[Ghost25]

How would somebody neutralize this stuff if they want to throw their bottle away safely?

If you want to dispose of any household chemical the proper way, find your local household hazardous materials disposal site. Most counties have them for paints/pesticides/cleaning products. Much of it is probably incinerated.

Just for fun, if you have any bodywash, check the label. All three of my housemates bodywashes contain polyquaternium 7. Nothing wrong with that, but it's all around us.