Exhibit 24.2

         LIMITED POWER OF ATTORNEY FOR SECTION 16 REPORTING OBLIGATIONS

    The undersigned hereby constitutes and appoints Sarah P. Cecil the
undersigned's true and lawful attorney-in-fact to:

          (1)     execute for and on behalf of the undersigned, in the
                  undersigned's capacity as a director, officer and/or
                  stockholder of a class of securities of Metabolix, Inc.
                  (the "Company"), as the case may be, Forms 3, 4 and 5,
                  and amendments thereto, in accordance with Section 16(a)
                  of the Securities Exchange Act of 1934, as amended (the
                  "Exchange Act"), and the rules thereunder;

          (2)     do and perform any and all acts for and on behalf of the
                  undersigned which may be necessary or desirable to
                  complete and execute any such Form 3, Form 4 or Form 5,
                  or amendments thereto, and timely file such form with
                  the Securities and Exchange Commission and any stock
                  exchange or similar authority; and

          (3)     take any other action of any type whatsoever in
                  connection with the foregoing which, in the opinion of
                  such attorney-in-fact, may be necessary or desirable in
                  connection with the foregoing authority, it being
                  understood that the documents executed by such
                  attorney-in-fact on behalf of the undersigned, pursuant
                  to this Power of Attorney shall be in such form and
                  shall contain such terms and conditions as such
                  attorney-in-fact may approve.

    The unersigned hereby grants to such attorney-in-fact full power and
authority to do and perform all and every act and thing whatsoever requisite,
necessary, or proper to be done in the exercise of any of the rights and powers
herein granted, as fully to all intents and purposes as such attorney-in-fact
might or could do if personally present, with full power of substitution or
revocation, hereby ratifying and confirming all that such attorney-in-fact, or
his or her substitute or substitutes, shall lawfully do or cause to be done by
virtue of this Power of Attorney and the rights and powers herein granted. The
undersigned acknowledges that the foregoing attorney-in-fact, in serving in such
capacity at the request of the undersigned, is not assuming, nor is the Company
assuming, any of the undersigned's responsibilities to comply with Section 16 of
the Exchange Act.

    This Power of Attorney shall remain in full force and effect until the
undersigned is no longer required to file Forms 3, 4 and 5 with respect to the
undersigned's holdings of, and transactions in, securities issued by the
Company, unless earlier revoked by the undersigned in a signed writing delivered
to the foregoing attorneys-in-fact. This Power of Attorney may be filed with the
Securities and Exchange Commission as a confirming statement of the authority
stated herein.

    IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to
be executed as of this 29th day of August, 2014.

                                        BIRCHVIEW CAPITAL, LP

                                        By:  /s/Matthew Strobeck
                                             -------------------
                                        Name: Matthew Strobeck
                                        Title: Partner