Document:

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                                                                    EXHIBIT 4.16

                            2000 TERM PROMISSORY NOTE

$3,000,000.00                                              Boston, Massachusetts
                                                           March 28, 2000

         FOR VALUE RECEIVED, the undersigned, (collectively, the "Debtors"),
hereby unconditionally and jointly and severally promise to pay to the order of
CONGRESS FINANCIAL CORPORATION (NEW ENGLAND), a Massachusetts corporation (the
"Payee"), at the offices of Payee at One Post Office Square, Boston,
Massachusetts 02109, or at such other place as the Payee or any holder hereof
may from time to time designate, the principal sum of THREE MILLION DOLLARS
($3,000,000.00) in lawful money of the United States of America and in
immediately available funds, in thirty-six (36) consecutive monthly installments
(or earlier as hereinafter provided) on the first day of each month commencing
May 1, 2000 of which the first thirty-five (35) installments shall each be in
the amount of EIGHTY THREE THOUSAND THREE HUNDRED THIRTY THREE DOLLARS AND
THIRTY-THREE CENTS ($83,333.33), and the last installment shall be in the amount
of the entire unpaid balance of this Note.

         Each Debtor hereby further promises jointly and severally to pay
interest to the order of Payee on the unpaid principal balance hereof at the
Interest Rate. Such interest shall be paid in like money at said office or place
from the date hereof, commencing April 1, 2000 and on the first day of each
month thereafter until the indebtedness evidenced by this Note is paid in full.
Interest payable upon and after an Event of Default or termination or
non-renewal of the Loan Agreement shall be payable upon demand.

         For purposes hereof,

         a) The term "Interest Rate" shall mean, as to Prime Rate Loans, a rate
of one and one-half (1.5%) percent per annum in excess of the Prime Rate, and as
to Eurodollar Rate Loans, a rate of three (3.0%) percent per annum in excess of
the Adjusted Eurodollar Rate; provided, that, at Payee's option, the Interest
Rate shall mean a rate of four (4.0%) percent per annum in excess of the Prime
Rate as to Prime Rate Loans and a rate of five and one-half (5.5%) percent per
annum in excess of the Adjusted Eurodollar Rate as to Eurodollar Rate Loans upon
and after an Event of Default or termination or non-renewal of the Loan
Agreement,

         b) The term "Prime Rate" shall mean the rate from time to time publicly
announced by First Union National Bank, or its successors, as its prime rate,
whether or not such announced rate is the best rate available at such bank,

         c) The term "Event of Default" shall mean an Event of Default as such
term is defined in the Loan Agreement, and

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         d) The term "Loan Agreement" shall mean the Loan and Security
Agreement, dated May 8, 1995, as amended, between Debtors and Payee, as the same
now exists or may hereafter be amended, modified, supplemented, extended,
renewed, restated or replaced.

         Unless otherwise defined herein, all capitalized terms used herein
shall have the meaning assigned thereto in the Loan Agreement.

         The Interest Rate applicable to Prime Rate Loans payable hereunder
shall increase or decrease by an amount equal to each increase or decrease,
respectively, in the Prime Rate, effective on the first day of the month after
any change in the Prime Rate is announced. The increase or decrease shall be
based on the Prime Rate in effect on the last day of the month in which any such
change occurs. Interest shall be calculated on the basis of a three hundred
sixty (360) day year and actual days elapsed. In no event shall the interest
charged hereunder exceed the maximum permitted under the laws of the
Commonwealth of Massachusetts or other applicable law.

         This Note is issued pursuant to the terms and provisions of the Loan
Agreement to evidence the 2000 Term Loan by Payee to Debtors. This Note is
secured by the Collateral described in the Loan Agreement and all notes,
guarantees, security agreements and other agreements, documents and instrument
now or at any time hereafter executed and/or delivered by any Debtor or any
other party in connection therewith (all of the foregoing, together with the
Loan Agreement, as the same now exist or may hereafter be amended, modified,
supplemented, renewed, extended, restated or replaced, being collectively
referred to herein as the "Financing Agreements"), and is entitled to all of the
benefits and rights thereof and of the other Financing Agreements. At the time
any payment is due hereunder, at its option, Payee may charge the amount thereof
to any account of any Debtor maintained by Payee.

         If any payment of principal or interest is not made when due hereunder,
or if any other Event of Default shall occur for any reason, or if the Loan
Agreement shall be terminated or not renewed for any reason whatsoever, then and
in any such event, in addition to all rights and remedies of Payee under the
Financing Agreements, applicable law or otherwise, all such rights and remedies
being cumulative, not exclusive and enforceable alternatively, successively and
concurrently, Payee may, at its option, declare any or all of Debtors'
obligations, liabilities and indebtedness owing to Payee under the Loan
Agreement and the other Financing Agreements (the "Obligations"), including,
without limitation, all amounts owing under this Note, to be due and payable,
whereupon the then unpaid balance hereof, together with all interest accrued
thereon, shall forthwith become due and payable, together with interest accruing
thereafter at the then applicable Interest Rate stated above until the
indebtedness evidenced by this Note is paid in full, plus the costs and expenses
of collection hereof, including, but not limited to, attorneys' fees and legal
expenses.

         Each Debtor (i) waives diligence, demand, presentment, protest and
notice of any kind, (ii) agrees that it will not be necessary for Payee to first
institute suit in order to enforce payment of this Note and (iii) consents to
any one or more extensions or postponements of time of payment, release,
surrender or substitution of collateral security, or forbearance or other

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indulgence, without notice or consent. The pleading of any statute of
limitations as a defense to any demand against Debtor is expressly hereby waived
by each Debtor. Upon any Event of Default or termination or non-renewal of the
Loan Agreement, Payee shall have the right, but not the obligation to setoff
against this Note all money owed by Payee to any Debtor.

         Payee shall not be required to resort to any Collateral for payment,
but may proceed against any Debtor and any guarantors or endorsers hereof in
such order and manner as Payee may choose. None of the rights of Payee shall be
waived or diminished by any failure or delay in the exercise thereof.

         The validity, interpretation and enforcement of this Note and the other
Financing Agreements and any dispute arising in connection herewith or therewith
shall be governed by the internal laws of the Commonwealth of Massachusetts
(without giving effect to principles of conflicts of law).

         Each Debtor irrevocably consents and submits to the non-exclusive
jurisdiction of the Courts of the Commonwealth of Massachusetts and the United
States District Court for the District of Massachusetts and waives any objection
based on venue or FORUM NON CONVENIENS with respect to any action instituted
therein arising under this Note or any of the other Financing Agreements or in
any way connection with or related or incidental to the dealings of Debtors and
Payee in respect of this Note or any of the other Financing Agreements or the
transactions related hereto or thereto, in each case whether now existing or
hereafter arising, and whether in contract, tort, equity or otherwise, and
agrees that any dispute arising out of the relationship between Debtor and Payee
or the conduct of such persons in connection with this Note or otherwise shall
be heard only in the courts described above (except that Payee shall have the
right to bring any action or proceeding against any Debtor or its property in
the courts of any other jurisdiction which Payee deems necessary or appropriate
in order to realize on the Collateral or to otherwise enforce its rights against
Debtor or its property).

         Each Debtor hereby waives personal service of any and all process upon
it and consents that all such service of process may be made by certified mail
(return receipt requested) directed to it and service so made shall be deemed to
be completed five (5) days after the same shall have been so deposited in the
U.S. mails, or, at Payee's option, by service upon Debtor in any other manner
provided under the rules of any such courts. Within thirty (30) days after such
service, Debtors shall appear in answer to such process, failing which Debtor
shall be deemed in default and judgment may be entered by Payee against Debtors
for the amount of the claim and other relief requested.

         EACH DEBTOR WAIVES ANY RIGHT TO TRIAL BY JURY OF ANY CLAIM, DEMAND,
ACTION OR CAUSE OF ACTION (i) ARISING UNDER THIS NOTE, OR (ii) IN ANY WAY
CONNECTED WITH OR RELATED OR INCIDENTAL TO THE DEALINGS BETWEEN DEBTOR AND PAYEE
IN RESPECT OF THIS NOTE OR ANY OF THE OTHER FINANCING AGREEMENTS OR THE
TRANSACTIONS RELATED HERETO OR THERETO IN EACH CASE WHETHER NOW EXISTING OR
HEREAFTER ARISING, AND WHETHER IN CONTRACT, TORT, EQUITY OR OTHERWISE. DEBTOR
AGREES AND

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CONSENTS THAT ANY SUCH CLAIM, DEMAND, ACTION OR CAUSE OF ACTION SHALL BE DECIDED
BY COURT TRIAL WITHOUT A JURY.

         The execution and delivery of this Note has been authorized by the
Board of Directors and by any necessary vote or consent of the stockholders of
Debtors. Each Debtor hereby authorizes Payee to complete this Note in any
particulars according to the terms of the loan evidenced hereby.

         This Note shall be binding upon the successors and assigns of each
Debtor and inure to the benefit of Payee and its successors, endorsees and
assigns. Whenever used herein, the term "Debtor" shall be deemed to include its
successors and assigns and the term "Payee" shall be deemed to include its
successors, endorsees and assigns. If any term or provision of this Note shall
be held invalid, illegal or unenforceable, the validity of all other terms and
provisions hereof shall in no way be affected thereby.

<TABLE>
<S>                                                    <C>
ATTEST:                                                CLEAN HARBORS ENVIRONMENTAL SERVICES, INC.

/s/ C. MICHAEL  MALM                                   By:   /s/ STEPHEN MOYNIHAN
------------------------------------                       -----------------------------------
Secretary
[Corporate Seal]                                       Title: SENIOR VICE PRESIDENT
                                                              --------------------------------

ATTEST:                                                CLEAN HARBORS KINGSTON FACILITY CORPORATION

/s/ C. MICHAEL  MALM                                   By: /s/ STEPHEN MOYNIHAN
------------------------------------                       -----------------------------------
Secretary
[Corporate Seal]                                       Title: SENIOR VICE PRESIDENT
                                                              --------------------------------

ATTEST:                                                CLEAN HARBORS OF BRAINTREE, INC.

/s/ C. MICHAEL  MALM                                   By:  /s/ STEPHEN MOYNIHAN
------------------------------------                       -----------------------------------
Secretary
[Corporate Seal]                                       Title: SENIOR VICE PRESIDENT
                                                              --------------------------------
</TABLE>

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<TABLE>
<S>                                                    <C>
ATTEST:                                                CLEAN HARBORS SERVICES, INC.

/s/ C. MICHAEL  MALM                                   By: /s/ STEPHEN MOYNIHAN
------------------------------------                       -----------------------------------
Secretary
[Corporate Seal]                                       Title: SENIOR VICE PRESIDENT
                                                              --------------------------------

ATTEST:                                                CLEAN HARBORS OF NATICK, INC.

/s/ C. MICHAEL  MALM                                   By: /s/ STEPHEN MOYNIHAN
------------------------------------                       -----------------------------------
Secretary
[Corporate Seal]                                       Title: SENIOR VICE PRESIDENT
                                                              --------------------------------

ATTEST:                                                CLEAN HARBORS OF CONNECTICUT, INC.

/s/ C. MICHAEL  MALM                                   By: /s/ STEPHEN MOYNIHAN
------------------------------------                       -----------------------------------
Secretary
[Corporate Seal]                                       Title: SENIOR VICE PRESIDENT
                                                              --------------------------------

ATTEST:                                                MURPHY'S WASTE OIL SERVICE, INC.

/s/ C. MICHAEL  MALM                                   By: /s/ STEPHEN MOYNIHAN
------------------------------------                       -----------------------------------
Secretary
[Corporate Seal]                                       Title: SENIOR VICE PRESIDENT
                                                              --------------------------------

ATTEST:                                                MR. FRANK, INC.

/s/ C. MICHAEL  MALM                                   By: /s/ STEPHEN MOYNIHAN
------------------------------------                       -----------------------------------
Secretary
[Corporate Seal]                                       Title: SENIOR VICE PRESIDENT
                                                              --------------------------------

ATTEST:                                                SPRING GROVE RESOURCE RECOVERY, INC.
</TABLE>

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<TABLE>
<S>                                                    <C>
/s/ C. MICHAEL  MALM                                   By: /s/ STEPHEN MOYNIHAN
------------------------------------                       -----------------------------------
Secretary
[Corporate Seal]                                       Title: SENIOR VICE PRESIDENT
                                                              --------------------------------

ATTEST                                                 HARBOR MANAGEMENT CONSULTANTS, INC.

/s/ C. MICHAEL  MALM                                   By: /s/ STEPHEN MOYNIHAN
------------------------------------                       -----------------------------------
Secretary
[Corporate Seal]                                       Title: SENIOR VICE PRESIDENT
                                                              --------------------------------
</TABLE>

                                      -6-<PAGE>

                                                                  EXHIBIT 10.24

[Letterhead]

BIOTRANSPLANT
------------- [LOGO]
INCORPORATED

December 1, 1998
                                                        Building 75, 3rd Avenue
                                                          Charlestown Navy Yard
                                                          Charlestown, MA 02129
                                                              Tel: 617/241-5200
                                                               FAX 617/241-8780
David H. Sachs, M.D.
Director, Transplantation Biology
Research Center
Department of Surgery
Massachusetts General Hospital
Charlestown, MA 02129

Dear David:

As January 1, 1999 completes eight years of your consulting arrangements with
us, BioTransplant is pleased to renew your contract for the coming year
(1/1/99-1/1/2000). Per our agreement, the consumer price index increased by
1.5% and the consulting rate is $92,704.00 for the coming year.

Please sign both copies of this letter, return one copy to me and keep the
other for your records.

David, based on all the hard work that we've done to date, 1999 should
finally achieve our proof of principle!

Best Wishes,

/S/ Elliot Lebowitz
--------------------------
Elliot Lebowitz, Ph.D.
President and CEO

Accepted by:

/S/ David H. Sachs
--------------------------
David H. Sachs, M.D.

12/15/98
--------------------------
Date

<PAGE>

[Letterhead]

BIOTRANSPLANT
------------- [LOGO]
INCORPORATED

January 5, 2000
                                                        Building 75, 3rd Avenue
                                                          Charlestown Navy Yard
                                                          Charlestown, MA 02129
                                                              Tel: 617/241-5200
                                                               FAX 617/241-8780
David H. Sachs, M.D.
Professor of Surgery (Immunology), Harvard Medical School
Director, Transplantation Biology Research Center
Massachusetts General Hospital
MGH-East, Building 149-9019, 13th Street
Boston, MA 02129

Dear David:

As January 1, 2000 completes nine years of your consulting arrangements with
us, BioTransplant is pleased to renew your contract for the coming year
(1/1/2000-1/1/2001). Per our agreement, the consumer price index increased by
2.7% and the consulting rate is $95,207.00 for the coming year.

Please sign both copies of this letter, return one copy to me and keep the
other for your records.

David, based on all the hard work that we've done to date, 2000 should
finally achieve our proof of principle!

Best Wishes,

/S/ Elliot Lebowitz
--------------------------
Elliot Lebowitz, Ph.D.
President and CEO

Accepted by:

/S/ David H. Sachs
------------------------------
Name

1/11/2000
---------------------------
Date

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