Table 2. Method detection limits and EPA primary drinking water quality standards

Sorption and Leaching of Trace-Level Metals by Polymeric Well Casings

MATERIALS AND METHODS - SR96_080008

SR96_08
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Table 2. Method detection limits and EPA primary drinking water

of organic constituents from these

quality standards (Maximum Contaminant Levels [MCLs]).

materials (Ranney and Parker 1994).

In these studies, we compared these

MDL

EPA primary drinking water std.

four materials with two other com-

monly used polymeric well casing

g/L

Metal

materials, PVC and PTFE. The results

0.010

from these two studies are summa-

0.41

1.5

rized in Table 1. The results for sorp-

tion of organic solutes agree fairly

0.059

0.064

well with Gillham and O'Hannesin's

0.12

0.7

100

(1990) findings, except that they

0.37

1000

1300

found FRE to be more sorptive of or-

0.66

100

0.35

0.89

ganic solutes than rigid PVC, and we

8.5

did not (Ranney and Parker 1994).

0.19

We believe the reason their findings

Given in the Federal Register (1975).

differed slightly from ours is because

Given in US EPA (1994).

they tested FRE tubing and PVC pipe

while we tested well casings made for monitoring

several cations (Cd, Pb, and Fe) occurred in some

wells. It was decided to eliminate ABS from fur-

samples exposed to PTFE (and PVC) screen, al-

though these losses were substantially less than

ther consideration since our studies (Ranney and

those observed for SS screens (Hewitt 1994).

Parker 1994, 1995) had shown the ABS tested

(waste and vent pipe) was not a good material for

With respect to the literature on leaching of met-

monitoring organic contaminants and because

als from FEP, FRE, or FRP, only one relevant labo-

ABS well casing was no longer available.

ratory study (Cowgill 1988) was found. Cowgill

To determine the overall suitability of FEP, FRE,

searched for 30 elements in water samples that

and FRP for groundwater monitoring wells, it is

had been exposed to a ground powder of FRE

also important to assess whether these materials

well casings. Apparently, no elements leached af-

sorb or leach metals. A review of the literature on

ter 72 hours' exposure, but after three weeks, mg/

L levels of B and Cl and g/L levels of P, Mg, and

sorption and leaching of metals by these products

Zn were found in the leachate. These concentra-

produced relatively little information.

tions were all below the EPA's drinking water stan-

According to Masse et al. (1981) anions do not

dards or else were not regulated.

strongly associate with polymer surfaces such as

Although no other studies were found for FEP

polyethylene (PE) and PTFE. Hewitt (Parker et al.

and FRP, we expect that FEP may behave similar-

1990, Hewitt 1992) observed that PTFE and rigid

ly to PTFE. Hewitt (Hewitt 1989, 1992) reported

PVC did not sorb the anionic forms of As and Cr.

that under static conditions PTFE leached sub-

However, sorption of cations by these polymers

stantially less of some metals than rigid PVC and

does appear to occur (Masse et al. 1981, Parker et

especially SS well casings. Under dynamic condi-

al. 1990, Hewitt 1992). Only one laboratory study

tions, concentrations of several metals (Cd, Cr,

(Raber et al. 1983) was found that specifically ad-

Cu, Fe, Ni, Pb) in samples exposed to PTFE (and

dressed sorption of metals by any of these three

PVC) well screens did not differ from the controls

materials. Raber et al. (1983) tested twelve differ-

(Hewitt 1994).

ent polymers for sorption of three radionuclides

2+, and Cs+) and found that FEP and

( SeO3 -, Sr

In this report, we will compare sorption and

leaching of metal species by FEP, FRE, FRP, PTFE,

PTFE were among the least sorptive materials.

and PVC. In the leaching study 11 metals (Ag, As,

Several studies (Hewitt 1989, Parker et al. 1990,

Ba, Be, Cd, Cr, Cu, Pb, Ni, Se, and Zn) will be

Hewitt 1992, 1994) have assessed sorption of met-

sought. With the exception of Ba, all these metals

als by PTFE. Since FEP and PTFE are both fluo-

are on the EPA's priority pollutant list. Also, the

ropolymers, data for PTFE may indicate how FEP

US EPA has established maximum contaminant

will perform. These studies show that under stat-

levels (MCLs) in drinking water (US EPA 1994)

ic conditions there was relatively little sorption of

for all these metals except Ag and Zn (Table 2). In

several cations (Pb, Cd, Cu, Fe) by PTFE when

the sorption study, these five casing materials were

compared with rigid PVC and especially SS cas-

exposed to a solution containing a mixture of g/

ings (Parker et al. 1990, Hewitt 1992). However,

L concentrations of As, Cd, Cr, and Pb.

under dynamic conditions, significant losses of

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