Boric Acid Remains in Watermaker Water

[Katiusha]

Looks like RO process (watermakers) doesn't filter out boric acid very well. Seawater contains 4.5 mg/L, whereas WHO and USEPA guidelines state 1 mg/L and 0.5 mg/L:

http://www.trusselltech.com/media/1.pdf [pdf]
http://www.lenntech.com/processes/de...on-removal.htm
Boron rejection by cellulose acetate reverse osmosis membranes 10.1016/S0011-9164(00)80079-X : Desalination | ScienceDirect.com
Problems with desalination plants - Ockham's Razor - ABC Radio National (Australian Broadcasting Corporation)

The most sensitive to increased boric acid content in the water would be pregnant women and children. Though long term effects can be damaging to adults as well.

This problem has been known for some time and industrial RO plants usually do a partial second pass (75%) to remove boric acid with probable ph adjustment in between. The reason for a partial pass is to make sure that the water is not completely demineralized.

Google more - there is a wealth of information on it.


So we are considering what to do with our watermaker setup: setup a partial second pass with a Y valve or add a boric acid filtration resin on the way to the tank (not sure of the cost).

Has anyone gotten concerned with this problem? What is your setup?

[Tellie]

Industrial second pass systems consist of a second low energy membrane designed specifically for it and re-routing the concentrate back to the SW membrane. Your watermaker would have to be able to compensate for the added pressures and flows required. Most all watermakers are designed for the membrane used, they are not designed for an extra membrane of any kind. Re-running your initial product water via a Y valve would be extremly inefficent and cost prohibitive to a boat based RO system. Remember your gallon of product water made is a result of passing far more gallons across the membrane surface. I like to use the 10 to 1 ratio for easy math, ratios vary widely depending on the machine. But for every gallon of product water made it will take ten gallons of sea water to do it. To re-run your product water through your watermakers membrane again as you suggest via a Y valve would mean the same 10 to 1 ratio. The ratio would be a bit less because you are now running fresh water through SW membrane but the inefficenciy is still far too huge. So keeping the 10 to 1 ratio in mind, you run your watermaker to make 100 gallons of product water diverted to your tank. You now want to re-route that 100 gallons back through the watermaker for a so called second pass and you end up with a little over 10-12 gallons in your tank and dumping 88-90 gallons of first run product water overboard through the brine discharge. It's just not practical. Finding a boric acid filtration media set up for a small boat might be interesting, I've never seen one but that doesn't mean they don't exsist. If they do exisit I would think it would have to have it's own pumping system separate from the watermaker. I just don't see that as practical but on much larger craft. But your concernes are worth loking at. But remember you'r more likely to encounter and injest far more nasties floating in sea water on a single snorkel trip than you are in months worth of RO water injested. If you clean your own hull forgitaboutit.

[Katiusha]

Tellie, thanks for your thoughts on this. Didn't think of the second pass losses...

We're not so concerned about ingesting the stuff ourselves. But our new baby will be arriving at around the same time as a new watermaker. She'll be cruising with us from her birth, so it's more of a concern for her. We want to give her a bit of time to grow before getting her to clean the hull

Regarding other treatment options: I found this ion exchange resin: Lanxess Lewatit MK 51. But for some reason it's marketed as a Waste Water Treatment: Lanxess Lewatit ions exchange resins. Not sure it's the right scale for boat installation, whether it would work, and how much it costs, but I'll try to contact them.

[familycruisers]

We use the nursing water from Walgreens , gallon is a couple bucks. She breast feeds so gallon is only used for supplement drinks and mixing cereal. One gallon last 3 weeks. She is 8 months now, but we've been supplementing cereal since she was six weeks. (amazing how well they sleep if you slip a tablespoon or so of cereal in a bedtime bottle.)

[GordMay]

Seawater contains approximately 4-5 ppm boron.

The human body contains approximately 0.7 ppm of boron, and daily intake is approximately 2 mg.

At a daily intake of over 5 g of boric acid, the human body is clearly negatively influenced, causing nausea, vomiting, diarrhoea and blood clotting. Amounts over 20 g are life threatening.

It seems, to me, that she'd have to drink an AWFUL lot of R/O water, to approach a dangerous level of boron.

[Astrid]

If I understand correctly, boron is is a dietary necessity for mitosis in many edible plants and as a consequence human intake is approximately 2mg/day from food stuffs. Boron is present in virtually all water, and in seawater the amount is approximately 5ppm, well below toxicity levels. On the average, the human body normally contains .7ppm boron or borate. Ingestion of 5mg/day would be considered toxic.

That said, reverse osmosis will not usually remove boron or borate compounds, though it will remove most really dangerous contaminates. As a back up to water produced by your water maker, both Aqua Pure and PUR home water filtration systems remove or reduce the amount of boron, among other things, in one's drinking water.

[Astrid]

Darn, Gord beat me to it while I was going over my notes.

[Katiusha]

GordMay, EU and WHO recommend at most 0.5 and 1 mg per day additional intake as safe for adults.

By drinking 0.5 liter of watermaker's water, she would exceed EU and WHO guidelines for adults by almost 5 and 2.5 times respectively. That was the reason for my concern.

Astrid, thank you for pointing me towards Aqua Pure filters. ... and we just got a new Seagull setup, though Seagull does not filter out boric acid (based on their email response). Maybe we'll change or combine both.

familycruisers, thanks for the idea on carrying extra water and the cereal - very useful to know


Thanks to all of you for replying!

[Katiusha]

Just a bit more info from wikipedia:

Based on mammalian median lethal dose (LD50) rating of 2,660 mg/kg body mass, boric acid is poisonous if taken internally or inhaled in large quantities. The Thirteenth Edition of the Merck Index indicates that the LD50 of boric acid is 5.14 g/kg for oral dosages given to rats, and that 5 to 20 g/kg has produced death in adult humans. The LD50 of salt is reported to be 3.75 g/kg in rats according to the Merck Index.
Long term exposure to boric acid may be of more concern, causing kidney damage and eventually kidney failure (see links below). Although it does not appear to be carcinogenic, studies in dogs have reported testicular atrophy after exposure to 32 mg/kg bw/day for 90 days. This level is far lower than the LD50.[4]
According to boric acid IUCLID Dataset published by the European Commission, boric acid in high doses shows significant developmental toxicity and teratogenicity in rabbit, rat, and mouse fetuses as well as cardiovascular defects, skeletal variations, mild kidney lesions.[5] As a consequence, in August 2008, in the 30th ATP to EU directive 67/548/EEC, the EC decided to amend its classification as reprotoxic category 2 and to apply the risk phrases R60 (may impair fertility) and R61 (may cause harm to the unborn child).[6][7][8][9][10]
At a recent European Diagnostics Manufacturing Association (EDMA) Meeting several new additions to the Substance of Very High Concern (SVHC) candidate list in relation to the Registration, Evaluation, Authorisation and restriction of Chemicals Regulations 2007 (REACH) were discussed. The registration and review completed as part of REACH has meant the current classification of Boric Acid CAS 10043-35-3 / 11113-50-1 as of 1 December 2010 will be listed as H360FD (May damage fertility. May damage the unborn child.) [11][12]

[GordMay]

I don’t mean to belittle your laudable concern for your baby’s health. You've GOT TO get this right.
At 5 parts per million boron (0.0005%), wouldn’t you have to drink about
0.5 ÷ 0.000005 = 1,000,000 grams (26.4 gallons) of water, per day to consume 0.5 grams of boron? Or is my arithmetic screwed up, again?

[Katiusha]

Originally Posted by GordMay

I don’t mean to belittle your laudable concern for your baby’s health. You've GOT TO get this right.
At 5 parts per million boron (0.0005%), wouldn’t you have to drink about
0.5 ÷ 0.000005 = 1,000,000 grams (26.4 gallons) of water, per day to consume 0.5 grams of boron? Or is my arithmetic screwed up, again?

Thanks for persisting with this, GordMay.


Your arithmetic looks correct.

However I think we're using different reference numbers for amount of boric acid in sea water: you quote 5 ppm, I quote 5 mg/L (another article at http://www.desline.com/articoli/8121.pdf). WHO guidelines are in mg/L (maximum of 1 mg/L per day) as well.

I thought that if I keep the same units of measure to identify amount in seawater and maximum suggested amount, it would work out. Is it wrong?

[GordMay]

Originally Posted by Katiusha

... I think we're using different reference numbers for amount of boric acid in sea water: you quote 5 ppm, I quote 5 mg/L ...
... I thought that if I keep the same units of measure to identify amount in seawater and maximum suggested amount, it would work out. Is it wrong?

You are right to maintain consistent units of measure.
However, for water, 1 ppm = approximately 1 mg/L of contaminant in water.
Essentially, a measurement of 5 mg/L is the same as 5 ppm.

Notwithstanding, I don't see any harm in erring on the side of prudent caution, and post-filtering your infant's water.

[hellosailor]

"you quote 5 ppm, I quote 5 mg/L "
The metric system is lousy for carpentry and many things but good at water. There are 1000 grams, one kilogram, of water in one liter. One milligram is 1/1000th of one gram, so if there are 5mg/L of boric acid, that is 5mg out of 1000*1000 mg, which is 5mg of boric acid in 1,000,000 mg of water, which is to say five parts per million.

Which is what Gord quoted. And assuming I didn't screw up MY math.

Kati, you might look for a "Zerowater" pitcher. They're being sold all over the US chain stores these days, it is like a Britta pitcher but claims to produce water with zero mineral contant, sold with a tester to prove it. I know, you need some minerals, but if you start with zero you can add your own as you please. Or use the zerowater to dilute the watermaker water.

[A "milli" gram ought to be a "killi" gram so there'd be no thousand/million confusion, but then the French would probably say the damned English had no right to use "million" when it wasn't a mille to begin with.]

[Tellie]

Just for further thought. I still recommend that all water coming from your fresh water tanks is fltered/purified before injestion for all on board, but especially if a baby is in the equation. The vast majority of fresh water tanks on boats are their own growing eco systems regardless of how good the water is that you put into the tank.

[Katiusha]

Originally Posted by Tellie

Just for further thought. I still recommend that all water coming from your fresh water tanks is fltered/purified before injestion for all on board, but especially if a baby is in the equation. The vast majority of fresh water tanks on boats are their own growing eco systems regardless of how good the water is that you put into the tank.

Thanks. We know about such eco-systems from our current boat, so getting a Seagull filter for the new one.