heavy metal toxicity?

[charles matthews]

Thank you for excellent research and article. I remain unsure that your work warrants the conclusion that heavy metal accumulation is having deleterious effects in aquariums and would value your response.

"Trace" metals in ocean water occur in small quantities because they are poorly soluble; presumably over time such material has deposited in marine substrates. In the aquarium metals are added in food such as fish meal, where concentrations are of course high compared to seawater. However, obviously the concentration of metals is not toxic in fishmeal, because of the sufficiency and nature of organic binding. If one were to continue to add fishmeal to an aquarium, one would not get metal toxicity; one would get accumulation of fishmeal. As long as detritus was not removed, I suspect sediments would grow to keep pace with binding ability to prevent metal toxicity. That is, I don't understand why sediments cannot continue to accept insoluble precipitates forever, and I don't think heavy metal poisoning of the bulk water occurs in natural systems.

So how is it that heavy metals accumulate in organisms if sediments can accept them indefinitely in nature and in aquaria? I think the way heavy metal poisoning may occur ecologically is if an excess of chemically derived heavy metals are added to a food web from the initial input and this effect is magnified up the food chain. I don't see how there is anything to be magnified if the concentration of heavy metals is balanced with sulfates and iron and other potential coprecipitates when it comes in as food. So it seems to me that we may be accumulating atolls in our aquariums, not toxic excesses, and that these precipitates are inert.

If heavy metal poisoning does occur, it may do so because of a lack of humic substances and particulate matter to bind metals released from the surface of the substrate through photoreduction, since skimmers remove these protective chelators (as well as the heavy metals). It seems likely to me that more binding sites are removed by skimmers than ligands.

A very thoughtful article and your response would be greatly appreciated.

 

[rshimek]

Re: heavy metal toxicity?

Originally posted by charles matthews

Hi,

"Trace" metals in ocean water occur in small quantities because they are poorly soluble;

This is not a general truism. They occur may in small quantities simply because they are found in small quantities in the Earth's crust. Copper is highly soluble, so is mercury, nickel, etc. Most of the metals dissolve readily.

However, obviously the concentration of metals is not toxic in fishmeal, because of the sufficiency and nature of organic binding.

Fishmeals, in many cases are certainly toxic. See some of the recent announcements about limiting fish consumption because of the build up of mercury in fish. The production of protein meal from fish and shell fish caught in polluted areas has resulted in many cases of human poisoning. These cases, in fact, are what drives environmental regulations.

If one were to continue to add fishmeal to an aquarium, one would not get metal toxicity; one would get accumulation of fishmeal.

Depending on the fish meal, one could well get metal toxicity. It depends on the fish meal.

As long as detritus was not removed, I suspect sediments would grow to keep pace with binding ability to prevent metal toxicity.

Bacterial processing of organic materials results the conditions resulting in metal binding. This process is self-limiting through time.

That is, I don't understand why sediments cannot continue to accept insoluble precipitates forever, and I don't think heavy metal poisoning of the bulk water occurs in natural systems.

Well, the sediment systems are not infinite in capacity, and heavy metal poisoning in natural systems is well documented. I refer you to your local large unversity library and suggest you simply start perusing such journals as Marine Biology, Marine Pollution Bulletin, as well as texts and references on environmental toxicology.

So how is it that heavy metals accumulate in organisms if sediments can accept them indefinitely in nature and in aquaria?

The sediments don't accept anything. The metals are generally bound immediately by organisms as means of detoxifying them.

So it seems to me that we may be accumulating atolls in our aquariums, not toxic excesses, and that these precipitates are inert.

I would be nice if this were true, but it simply doesn't work that way.

 

[Fredfish]

An interesting and informative article as usual. Thanks!

I would be interested to know how effective carbon and the Polyfilter are in removing metals from water. It is my understanding that they would need to remove both "free" metals and those bound to organics.

I seem to remember that you did not know the capabilities of the Polyfilter, and Eric Borneman suggested that carbon would adsorb both free and bound metals.

I would thing that a multi pronged attack on metals would work.

1. use filtering on newly made artficial salt water
2. regular filtering of tank water to adsorb whatever is possible
3. use as many organic export mechanisms as your tank can support (skimmer, algae...)

I don't think I will ever go skimmerless after this series of articles and I am in the process of adding a ATS style algae filter to the tank.

Filtering saltwater for water changes is simple.

Now its just a mater of setting everything up, running the tank for a while, and then getting the water tested to see where the levels of these metals are.

Out of curiosity, how would I know what the adsorbtion capacity of activated carbon is?

Fred.

 

[charles matthews]

heavy metal toxicity?

Thanks for your reply. Just a little more information would be helpful. I am familiar with some of the toxicology literature you refer to, but I have not seen an article in which I could separate the effects of adding heavy metal inputs to a natural system. Are you aware of evidence of heavy metal poisoning occurring in an estuary or other area uncontaminated by chemical inputs? You can see why your conclusion on this is confusing me.(By the way, I am a neurologist and am well aware of the medical literature on the alarming biological effects of these metals in small quantities).

The other question that still bothers me regards the idea that putting trace elements bound in food into an aquarium inevitably leads to enhanced biological activity. I understand that trace metals are soluble; what I meant to say is that they do not remain so in seawater because they form insoluble precipitates.

Basically what I don't understand about the idea of accumulation of toxic trace metals is, in the absence of putting in a toxic concentration of toxic metabolites in the first place, what is the mechanism of concentration in the aquarium? It still seems viable that the substrate itself could accumulate inert trace metal precipitates. For example, a dead whale in an estuary doesn't lead to metal poisoning.

The example of mercury poisoning in fish just isn't relevant to aquariums. That is an organomercurial poisoning.

If there is something basic I don't understand, I would appreciate your help with this.

 

[charles matthews]

heavy metal toxicity?

OK, let me make my questioning a little more clear. There is a ratio of heavy metals to, say, phosphorus, in living tissue. It seems to me that, so long as this ratio stays the same in detritus accumulation, the population of animals in the aquarium is protected. It would seem that, per heavy metal element, the issue is partly whether the compound containing the metal is inert, and partly the amount of surrounding organics which includes to a small degree living forms, and not in any significant way the ratio of heavy metals to living forms.

One way to look at it is to say that both phosphorus and heavy metals accumulate at the same rate. Unless metals accumulate at a higher rate than phosphates, or phosphates are removed at a higher rate than metals, or living things preferentially accumulate heavy metals to their detriment over inorganic detritus, then detritus accumulation in aquaria should be harmless with respect to heavy metals.



The idea here is that detritus, and humic substances, protect against heavy metal toxicity. This is supported by Walsted in her book, The Ecology of the Planted Aquarium. It would seem that heavy metal toxicity would occur when metals are added in excess as in medications; and when added in topoff water without acompanying organics so that they accumulate over time in excess while organics and humics are removed. In such cases it would seem likely that precipitation of heavy metal compounds on sand at the surface would be reworked poorly into deeper sediments, and may well be at risk for reuptake by algae and taken up by micrograzers. But aquaria where detritus is conserved, such as in mud filters without skimmers, which are heavily fed, and where presumably heavy metal levels are higher, there is no evidence such tanks do poorly. In general, the trend toward heavy feeding is against your concerns.

Thanks again for taking the time to consider my thoughts on this matter.

 

[rshimek]

Originally posted by Fredfish

Hi Fred,

It is my understanding that they would need to remove both "free" metals and those bound to organics.

Yes, that is my understanding as well.

I seem to remember that you did not know the capabilities of the Polyfilter, and Eric Borneman suggested that carbon would adsorb both free and bound metals.

Yes.

I would thing that a multi pronged attack on metals would work.

Yes, I think that, at present, that is the best strategy.

I don't think I will ever go skimmerless after this series of articles and I am in the process of adding a ATS style algae filter to the tank.

I think the more filtration we can put on tanks, the better.

Out of curiosity, how would I know what the adsorbtion capacity of activated carbon is?

I don't know, and this is really an important question. Activated carbon is a great adsorbing material, but we have no way of telling when it is saturated, nor do we have any information about the relative removal rates of various metals or other toxins.

 

[rshimek]

Re: heavy metal toxicity?

Originally posted by charles matthews

Hi

OK, let me make my questioning a little more clear. There is a ratio of heavy metals to, say, phosphorus, in living tissue.

No; for animals immersed in a medium containing heavy metals, this is not a fixed ratio, but is dependent upon the environmental concentrations. As these concentrations rise above normal levels, many/most organisms actively transport metals into their tissues and attempt to detoxify them.

It seems to me that, so long as this ratio stays the same in detritus accumulation, the population of animals in the aquarium is protected.

Unfortunately, "detritus" is not a passive nor inert substance. It is basically a series of organic and inorganic substrata covered in bacteria, other micro-organisms, algae, and animals. In other words, nothing remains constant or consistent in it.

It would seem that, per heavy metal element, the issue is partly whether the compound containing the metal is inert, and partly the amount of surrounding organics which includes to a small degree living forms, and not in any significant way the ratio of heavy metals to living forms.

In fact, it is very much the other way around. The organic material is by and large living or continuously turned over non-living material. In any case, the heavy metals are not likely found as precipitates outside of living tissues.

One way to look at it is to say that both phosphorus and heavy metals accumulate at the same rate.

NEITHER of these substances passively "accumulate." Phosphorus is a limiting nutrient for microalgae and bacteria, the amount of free phosphate ion in the water is determined by the populations of these organisms and their metabolic rates. Heavy metals, by their toxic nature, are important to organisms and for the organisms to survive if the concentrations of these toxic materials rises above the normal limits that the organisms evolved with, the organisms must attempt to detoxify them. If they don't or can't, they die.

 

[charles matthews]

toxic metals?

toxic metals?

Thanks for the time you have taken with me. I think you have raised a tremendously important issue regarding metal toxicity. I continue struggling to express concerns I have about where this is taking you.

You are struggling with the real issue of organics, and metal, accumulation, in deep sand bed coral dominated tanks. And I am not coming at it from the point of view that sand beds are the future of reef tanks at all. I am thinking of the work of Adey 1991 on heavy metals and algae scrubbers, and of Tyree in his book on captive sea squirt and sponge filtration, as well as Diana Walsted, regarding the role of detritus accumulation and meavy metal protection.

Basically, I don't see sand beds suffocating because of accumulating organics. Or- the sand part may be suffocating, but the mud part is growing just as it should be. I see this as a normal transition to a finer more mud based bed because a sediment bed wants to match the flow regime of the tank. And there is no reason why the organics cannot accumulate into the more estuatine enrivonment the flow regime desires. In my undistrubed tanks, my substrate grows into mud over years, covering the original aragonite and developing a mud detrital community. And this is the "atoll" I was referring to. And I don't see this as suffocating the sand bed creatures; constructed properly, this is a healthy transition for the tank, where the substrate is properly graded for the flow regime.

As I think more about what you are saying, it may well be that we are thinking about different possibilities, and different futures for marine tanks. What you see as toxicity for sand tanks is healthy estuarine beach building for me. If the future of marine tanks were more intervention, more outputs to balance more inputs, then I think this is very sad and frankly I think I am going to have to go. But I really think this "more output to avoid toxicity" situation is not the only possibility. There is also substrate accumulation, such as in Adey's settling traps or simply in mud based tanks(Adey called this "geological export" although it could as well be "import"), particulate filtering by sea squirts and sponges such as in Tyree's tanks, or organism export to avoid "organism toxicity".

Essentially, while heavy metals are an important issue, exhorting hobbyists to both feed more and draw out more is not necessarily the only response; and mangrove swamps full of organics are the very best places to find delicate larvae, not heavy metal poisoning. So the connection between accumulation of sustrate detritus and heavy metal poisoning is not related, in my understanding.

I would like to write a more thoughtful and lengthy response to your concern that outputs should be directed to prevent toxic contaminants. The recommendation may be a good one, but I an thinking that it may be more appropatiate to reconsider the deep sand bed setup itself rather than to work so hard on the export side and still worry about the sand bed turning to organic mud. I am thinking of drawing specificaly from Adey's work on heavy metals- he showed that algae scrubbers scrubbed heavy metals effectiely- and his notion of geological export, with a thought experiment of moving the algae scrubber and settling filter topologically back inside the reef, which would make his results applicable to analysis of a simple closed system.

Steve Tyree has cited references in which the exchange rates of certain lagoons are essentially, surprisingly, equivalent to closed systems; and that this suggests that there exists mechanisms for balance in closed systems. He is reporting water clarity rivaling Berlin systems without a skimmer, using squirts and sponges for particulatae scrubbers only. So humic substances apparently can be consumed in cryptic areas in the reef tank, although further work needs to be done. The history of reef aquariums is full of loss of faith in the ability of natural systems to correct themselves. It may be that putting food into a tank is toxic to sand beds but not to other ecosystems. I would greatly appreciate if you would be willing to formally critique this piece after I have had time to do it properly.

Thanks so much for your time, especially with exams and the holidays. Best wishes to you and your family!

 

[rshimek]

Hi Charles,

Well, the basic problems with some of the works that you have cited is that they are simply wrong. The exception is Adey's work which is correct, as he used algal scrubbers to remove the metals, and this is possible, albeit most reef aquarists don't use ATS systems.

Using sponges and tunicates somehow magically remove these materials from a closed system is simply biologically and physically impossible. Regardless, of this we are not dealing with closed systems and these materials will continue to accumulate with time. They cannot be "contained" and must be removed.