EXHIBIT
4.1

    


    Pure
Earth, Inc.

    One
Neshaminy Interplex, Suite 201

    Trevose,
PA 19053

    
       

      
        	 	August 18,
      2009


      

    

    


    VIA E-MAIL AND FEDERAL
EXPRESS

    Fidus
Mezzanine Capital, L.P.

    190 S.
LaSalle Street

    Suite
2140

    Chicago,
IL 60603

    Attention:
Fidus Capital

    


    Re:           Series B
Preferred Stock of Pure Earth, Inc.

    


    Ladies
and Gentlemen:

    


    Reference
is made to that certain (i) Investment Agreement among Pure Earth, Inc. (the
“Company”) and
Fidus Mezzanine Capital, L.P. 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.

    


    In
connection with the Sixth Amendment to that certain Credit and Security
Agreement dated as of October 24, 2006 by and among Wells Fargo Bank, National
Association (“Wells Fargo”), the Company and certain of its affiliates, we have
agreed that in lieu of making the Coupon payment to holders of Series B
Preferred Stock otherwise due on September 30, 2009 (the amount of such Coupon
payment, the “Coupon Amount”), the Company shall instead pay holders of Series B
Preferred Stock the Coupon Amount, plus interest thereon at the rate of fourteen
percent (14%) per annum, either:

    


    
      	
               
      

            	
              (a)

            	
              in
      one lump sum representing the full Coupon Amount plus accrued interest on
      November 30, 2009; or

            


    

    


    
      	
               
      

            	
              (b)

            	
              if
      the Company either (i) refinances its outstanding obligations to Wells
      Fargo with an alternative lender, or (ii) renews such obligations for an
      extended maturity date with Wells Fargo, in each case prior to such dates
      set forth in clause (a) above, then any unpaid portion of the Coupon
      Amount plus accrued interest thereon shall be paid on the date such
      refinancing or renewal is
consummated.

            


    


    
      
         


      

      
         


        
          

        

      

      
         


      

    

    


    Notwithstanding
the provisions of this letter, in the event that the full Coupon Amount plus
accrued interest is not paid as provided in the preceding paragraph, the Event
of Noncompliance  with respect to the failure of the Company to pay
the Coupon Amount on September 30, 2009 shall be deemed to have occurred on
September 30, 2009 and not on the date that the Company fails to comply with the
preceding paragraph.

    


    Please
indicate your agreement and acceptance of the terms hereof by returning a copy
of this letter to my attention via facsimile at (215) 639-8756 and the original
via overnight delivery service to my attention at Pure Earth, Inc., One
Neshaminy Interplex, Suite 201, Trevose, PA 19053.

    


    
      
        
          
            
              
                	 
      	
                        Very
      truly yours,

                      
	 
      	 
      	 
      
	 
      	
                        Pure
      Earth, Inc.

                      
	 
      	 
      	 
      
	 
      	
                        By:

                      	
                        /s/
      Brent Kopenhaver

                      
	 
      	 
      	
                        Brent
      Kopenhaver, Chairman of the Board

                      
	 
      	 
      	
                        Chief
      Financial
Officer

                      


              

            

          

        

      

    

    


    Agreed
and Acknowledged:

    


    FIDUS
MEZZANINE CAPITAL, L.P.

    


    
      
        
          
            	
                    By:

                  	
                    /s/  Edward H.
    Ross

                  
	
                    Name: 

                  	
                    Edward
      H. Ross

                  
	
                    Title:

                  	
                    Managing
      Partner

                  


          

        

      

    


    
      
         


      

      
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