Exhibit
4.1

    


    March 26,
2010

    


    Pure
Earth, Inc.

    Mr. Brent
Kopenhaver

    Chairman
and Chief Financial Offer

    One
Neshaminy Interplex, Suite 201

    Trevose,
PA  19053

    


    
      	  	
              RE:

            	
              Series
      B Preferred Stock of Pure Earth,
  Inc.

            


    

    


    Dear Mr.
Kopenhaver:

    


    Reference
is made to that certain Investment Agreement among Pure Earth, Inc. (the
“Company”) and Fidus Mezzanine Capital,L.P. (“Fidus”) dated as of March
4,2008(the “Investment Agreement”) and (ii) the Certificate
of  Incorporation of the Company, as amended and restated to date (the
“Certificate” and collectively, with the Investment Agreement, the”Investment
Documents”). Capitalized terms used but not otherwise defined herein shall have
the meanings ascribed to such terms in the Investment Documents.

    


    An Event
of Noncompliance occurred under Section 8.1(b) of the Investment Agreement as a
result of the failure of the Company t deliver the financial statements within
the time period required by the terms of Section 5.1(a) of the Investment
Agreement for the month of January, 2010.  The financial statements
were delivered on March 10, 2010 and Fidus herby waives this Event of
Noncompliance.

    


    Further,
Fidus agrees that in lieu of making the cash dividend coupon payment to holders
of the Company’s Series B Preferred Stock otherwise due on each of September 30,
2009, December 31, 2009 and March 31, 2010(the amount of such payments
collectively, the “Coupon Amount”) pursuant to the terms of the Company’s Series
B Preferred Stock, the Company shall instead pay holders of the Company’s Series
B Preferred Stock in cash the Coupon Amount, plus interest on the Coupon Amount
at the rate of fourteen percent (14%) per annum by June 15,
2010.


    
      
         


      

      
        
        

        
          

        

      

      
         


      

    


    Notwithstanding
the provisions of this letter, in the event that the full Coupon Amount plus all
accrued interest with respect to such Coupon Amount is not paid in cash as
provided above, the Event of Noncompliance with respect to the failure of the
Company to pay the Coupon Amount on September 30, 2009, December 31, 2009 or
March 31, 2010 shall be deemed to have occurred on each payment date
respectively, and not on the date that the Company fails to comply with the
preceding paragraph and all rights and remedies of the holders of the Series B
Preferred Stock with respect to such failure shall be and remain in full force
and effect as if the agreement in the immediately preceding paragraph had never
been in effect.  In particular, without limitation of the foregoing,
in the event that the Coupon Amount shall not been paid in full in cash by June
15, 2010, the default dividend rate of 18% per annum provided in the Investment
Documents shall be applicable from and after September 30, 2009 until the Coupon
Amount and all accrued dividends on the Series B Preferred Stock for subsequent
periods ending after March 31, 2010 then due and payable shall have been paid in
full in cash.

    


    
      
        	
                FIDUS
      MEZZANINE CAPITAL, L.P.

              
	 
      
	
                By:  Fidus
      Mezzanine Capital GP, LLC

              
	 
      
	
                By:

              	
                /s/ Edward H. Ross

              
	 
      
	
                  Edward
      H. Ross, Managing Partner

              


      

    

    


    
      
        	
                AGREED
      AND ACKNOWLEDGED:

              
	 
      
	
                PURE
      EARTH, INC.

              
	 
      
	
                By:

              	
                /s/ Brent Kopenhaver

              
	 
      	
                Brent
      Kopenhaver, Chairman of the Board

              
	 
      	
                Chief
      Financial Officer