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MEMORANDUM

June 29, 1995                                     DRAFT

To: Mike Baker

From: Don Cortes

Re: Immunoassay vs. Mobile Laboratory

                                 


I have had the opportunity to review materials regarding SW-846
Draft 4020, a rapid screening procedure for Polychlorinated
Biphenyls (PCBs) using immunoassay.  Draft 4020 is an
inexpensive, relatively simple procedure for use in screening
soil samples for polychlorinated biphenyls (PCBs) at a user's
defined detection level.  However, its use at Lemon Lane Landfill
requires careful consideration of some potential problems. What
follows is a comparison of using Draft 4020 on-site to another
potential option, EPA Method 8080 using an on-site mobile
laboratory.

I wish to first point out that EPA Draft 4020 has not yet been
promulgated, although it has been field tested and is expected to
be included as a method in Revision 3 of SW-846 this year.    EPA
Method 8080 is an official method, and has been extensively
employed since the early 1980s.  This having been said, I will
refer to the methods as simply EPA 4020 or EPA 8080 in the rest
of this memorandum.

Turn Around Time:

EPA Draft 4020 appears to be a significantly faster procedure. 
Vendors indicate that 1 sample can be tested in 30 minutes, and
as many as 17 samples in 60 minutes.  I suspect 10 samples in 60
minutes is a more reasonable expectation, however.

EPA Method 8080 can be performed at the rate of 1 sample in 60
minutes, or 20 samples in 24 hours, using a rapid extraction
procedure that saves sample preparation time at the expense of an
increased detection limit.  The detection limit using this
technique is 1 ppm in soil, which should be acceptable for most
applications.

As will be discussed further on, EPA Draft 4020 requires
confirmation using EPA Method 8080 on at least 10% of the samples
found to contain PCBs.  Because this confirmation must be sent to
an offsite laboratory,  the effective turn around time may be the
same for both methods, when considering turn around time in terms
of a daily batch of samples.  Of course, samples tested by EPA
Method 8080 do not need confirmation.




Cost

EPA 4020 is significantly cheaper than EPA 8080.  I estimate a
total cost for this project of $15,000, which includes:

     1.   $2500 for accessories.  This includes all the basic
          accessories needed, including a photometer.  

     2.   $1820 for equipment to test 250 samples.

     3.   $2400 for analyst at $15/hour, 20 days.

     4.   $5000 for 25 confirmation samples at $200 per sample
          (rush charge).

     5.   $2500 for method validation.  This includes the cost of
          15 samples at $150/sample for EPA 8080, and an analyst
          at $15/hour.

A mobile laboratory would cost about $35,000 for 20 days, 250
samples.  This cost is based on my experience as a mobile
laboratory manager, and consultation with current mobile
laboratory contractors.


Quality 


While EPA 4020 may offer the advantages of quick turn around time
and low cost, it pales to EPA 8080 in terms of quality.  

1.  Accuracy

     EPA and Immunoassay vendors explicitly state that EPA 4020
     results are to be considered   estimates only.  For
     accurate, precise results, EPA 8080 must be employed for
     each and every sample.  This is due to the fact that:

     A.   Quantitation is performed using a standard that is
          probably dissimilar to the actual composition of the
          PCB mix found.  There is no way to choose a similar
          standard without knowing what type of PCB is present in
          the sample, and EPA 4020 does not give that
          information.

     B.   There is no way to detect many conditions that lead to
          false positives or false negatives with EPA 4020.

     In this case, a false positive results when PCBs are
     reported present when actually they are not.  This may
     result from any compound other than a PCB that has a binding
     affinity for the antibodies that make up the solid phase of
     the reaction chamber.  A false positive may also result if
     any compounds or oils are present that prevent the enzyme
     conjugate from binding to the antibody sites.  There is no
     way to "see" this happening in the reaction chamber.  With
     EPA 8080, on the other hand, one can "see" the PCBs by
     looking at the chromatogram.  Each Arochlor mixture displays
     a unique pattern that no other chemical or mixture can
     exactly reproduce.  The chances of a reporting a false
     positive by EPA 8080 are therefore extremely low.

     A false negative is a result of "not detected" when in fact
     PCBs are present at greater than the user defined detection
     level.  Erroneous results can be caused by any compounds
     which are present in the sample which interfere with the
     affinity that a PCB molecule has for an antibody site, or
     any compounds that restrict the availability of an antibody
     site for the target analyte.  For example, the presence of
     oils can alter the statistical distribution of enzyme
     conjugate and PCBs that are competing for the antibodies. 
     Since calculations assume a fair randomness in this
     competitive inhibition reaction, the presence of oils can
     cause unpredictable results.  With EPA 8080 however,
     surrogate standards are employed with every analysis in
     order to verify recovery of target analytes.  When these
     surrogates fall outside of an acceptance range, the analysis
     is suspect and is repeated until the cause of the failure
     can be determined.  Thus the chances of reporting a false
     negative by EPA 8080 are extremely low.

     I believe that the risk of reporting a false negative when
     using EPA 4020 on landfill material is greater than when
     analyzing soil, and thus is much higher than indicated in
     the method.  This is because landfill material often
     contains high concentration of chemicals that may cause
     interferences.  Of course, the method must first be
     validated using soil that is characteristic of the sample
     that is to be analyzed.  Since landfill soil is non-homogeneous, 
     this presents a tricky problem.  Suffice it to
     say that validation of the method must be extensive in it's
     coverage of all possible interferences.


2.   Information

     As has been previously stated, EPA 4020 provides no
     information as far as which mixtures of PCBs are present. 
     This information is important in choosing appropriate
     calibration standards for accurate analysis and determining
     the likelihood migration in water systems and soil.  EPA
     8080 does provide this information.  In addition, if
     trichlorobenzenes or tetrachlorobenzenes are part of the
     dielectric fluid used in the capacitors (and they often
     are),  they can be detected with a slight modification of
     EPA 8080 GC temperature program.

3.   Detection.

     The lowest detection limit achievable by EPA 4020 is 1 ppm. 
     However, the conceptual sampling plan for Lemon Lane
     indicates that the detection limit will be set at 400 ppm. 
     I presume that this is because the contractor believes that
     only a presence/absence result can be obtained.  If this
     were true, the effective detection limit would be 400 ppm. 
     This would compare with EPA 8080 detection limit of 1 ppm
     (rapid extraction technique).

     I wish to point out, however, that Millipore's 4020 kit
     comes with 5 detection levels.  5 detection levels can also
     be used with the Ensys 4020 kit, and the additional cost
     would be no more than $50 for the whole project.  There is
     absolutely no good reason not to use all 5 of these levels. 
     A detection level could be set at 1, 50, 100, 400, and 1000
     ppm, for example.  Each sample would need to be read out a
     maximum of 2 extra times per sample, at the cost of an
     additional 30 seconds per sample.  While exact quantitation
     would still not be achieved, the result could be reported as
     either:

          Less than 1 ppm
          Between 1 and 50 ppm
          Between 50 and 100 ppm
          Between 100 and 400 ppm
          Between 400 and 1000 ppm, or
          Greater than 1000 ppm .

     This is as opposed to the options of :

          Less than 400 ppm
          Greater than 400 ppm.


General Quality Assurance Issues:  It is very important that
proper quality assurance protocol be followed.  Some important
points:

1.   The test kits have not been demonstrated over 90¿F.  A basic
     characteristic of antibodies and enzymes is that they
     denature (rendering them permanently useless) above a
     certain temperature.  Precautions should be taken to insure
     that the temperature of the tubes and conjugate solution at
     no time exceed 90¿F prior to or during analysis.  Thus, the
     equipment should not be kept in the car on a sunny day, in
     the field, or in a cooler that is in direct sunlight.  In
     any case, the temperature should be monitored.

2.   The accuracy and precision of this method must be assessed
     as part of the validation study.  This must be performed
     under the same conditions as the analysis of the samples and
     at no more than 10 times the anticipated detection limit. 
     Method Detection Limit (MDL) studies must take precision
     into account.

3.   Each analyst must be qualified to perform the tests.  There
     should be documentation as to how proficiency has been
     demonstrated.

All the important points of a quality assurance program cannot be
covered here.  However,  a comprehensive quality assurance
program must be in place if EPA 4020 is to be employed, just as
if testing were being performed in a mobile laboratory or an off-site 
laboratory.




Conclusion: 

     Because I do not know the objectives of the Lemon Lane
     sampling plan, I cannot comment on the appropriateness of
     either EPA 4020 or  EPA 8080.  It is clear, however, that
     EPA 4020 provides an inexpensive and quick method to
     determine the presence or absence of PCBs at user defined
     levels, at the cost of a slight to moderate reduction of
          confidence in analytical results.

Table 1: Comparison of Immunoassay vs. Mobile Laboratory for
PCBs in Soil



                        Immunoassay             Mobile Laboratory


TURN AROUND TIME
                1 samples/30 minutes           1 sample/ 60 minutes 
                17 samples/60                  20 samples/24 hours
                minutes(?)

COST
                $15,000 - TOTAL                $35,000 - 20 days 
                ($2550 - Accessories)
                ($1820 - 250 Samples)
                ($2400 - Analyst for 20 days)
                ($5000 - 25 Confirmation samples
                        @ $200/sample)
                ($2500 - Method Validation)

QUALITY
  Accuracy      Estimate only                   High accuracy
  Detection     400 ppm                         1 ppm (rapid extraction)
                Qualitative                     Identifies Arochlor
                PCB yes/no

  Risk of False     High                        Extremely low 
  Positives
  
  Risk of False    Moderate                     Extremely low 
  Negatives

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