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      UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
       	     WASHINGTON, D.C. 20460
      		
      
                         				OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION
                             OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION
       
   
                                         
   
   MEMORANDUM                                                                   August 31, 2012
   
SUBJECT:	Summary of Ecotoxicity Data for Cytokinin Registration Review Document
    
               EPA Reg. #:		5905-LIU
               CAS #:		              525-79-1 and 133-32-4 
               PC Code                             116801 and 116802
               		
   
   FROM:	Michael Rexrode, Ph.D., Senior Biologist          /s/             08/31/2012
               Biochemical Pesticides Branch
               Biopesticide & Pollution Prevention Division (7511P)
   
   TO:		Leonard Cole, Regulatory Action Leader   /s/                      08/31/2012
               Biochemical Pesticides Branch
               Biopesticide & Pollution Prevention Division (7511P)
   
         
         
         

ACTION REQUESTED

The following is the final ecotoxicity assessment for cytokinin/kinin in support of the Registration Review Decision Document.   


RECOMMENDATIONS AND CONCLUSIONS

Executive Summary
The plant regulator, cytokinin, was initially registered in the United States in 1978 as CYTEX(R) (EPA Reg. No. 35980-1) for applications to certain citrus, fruit and vegetable crops. Cytokinin acts as a plant regulator by promoting cell division; minimizing effects of stress; root stimulation; increased yield; increased vegetative growth; and increased tuber firmness.
During Phase 4 of the Reregistration Process, the data base for cytokinin was evaluated and determined to be inadequate in satisfying certain requirements for biochemical pesticides which include plant regulators. 

Since the DCI, the Agency's initial position about these data gaps was re-evaluated and all of these data requirements, except for 154-B-11 Non-target insects, were waived because available information indicates cytokinin does not cause unreasonable adverse effects: 1) The principal constituents of cytokinin, algae and seaweed, are natural components of fish diets; 2) Cytokinin has a very low acute mammalian toxicity; 3) Cytokinin is used as a dietary supplement in animal feeds; and 4) are expected to have no adverse effects to fish and wildlife.
During development of the reregistration eligibility decision (RED), the data requirements for non-target insect testing were re-examined and these data requirements were waived based on the previously mentioned rationale for ecological effects (i.e., low acute mammalian toxicity; use as a fish and animal food supplement; and lack of expected adverse effects to fish and wildlife). Therefore, the data are adequate to support the currently registered uses of cytokinin.

This Reregistration Eligibility Decision reflects a reassessment of all data which were submitted in response to the Reregistration Process. Based on the available information for cytokinin the Agency does not foresee the need for additional ecotoxicity data for a new risk assessment and has waived all hazard and exposure data on these chemicals. The unique characteristics of these products, there non-toxic mode of action, and biodegradability (low to no persistence), will not result in toxic risk to non-targets, including threatened and endangered species. The Agency considers cytokinin use to have a no effect (NE) on endangered/threatened species. 

Background
Cytokinin is generally found in higher concentrations in meristematic regions and growing tissues. They are believed to be synthesized in the roots and translocated via the xylem to shoots. Cytokinin biosynthesis happens through the biochemical modification of adenine. Cytokinins have been found in almost all higher plants as well as mosses, fungi, bacteria, and also in tRNA of many prokaryotes and eukaryotes. Today there are more than 200 natural and synthetic cytokinins combined. Cytokinin concentrations are highest in meristematic regions and areas of continuous growth potential such as roots, young leaves, developing fruits, and seeds (Arteca, 1996; Mauseth, 1991; Raven, 1992; Salisbury and Ross, 1992). 








Toxicology 
Summaries of the toxicology profile for cytokinin are shown in Table 1.0. Based on this information cytokinins are practically non-toxic to mammalian species (LD50 > 5,000 mg/kg) (Toxicology Cat. IV); can cause slight acute dermal effects (Toxicology Cat. III), and slight eye irritation (Toxicology Cat. III). Studies on kinetin (Table 2.0) show that the compound has a Toxicological Category IV for acute oral (LD50 > 5,000 mg/kg), Acute Dermal (LD50 > 5,000 mg/kg), Acute Inhalation (LC50 > 2.09 mg/L), and Dermal Irritation (non-irritating). The study on Eye Irritation showed mild effects and a Toxicology Category III.

Table 1.0. Acute Toxicological Values for Cytokinin 
                                   Guideline
                                     Study
                                    Results
                                   Category
                                    MRID #
                                   870.1100
                               Acute Oral (rat)
                             LD50 > 5,000mg/kg
                                      IV
                                   00142864
                                   870.1200
                                 Acute Dermal
                             LD50 > 2,000 mg/kg
                                      III
                                   00138093
                                   870.1300
                               Acute Inhalation
                                    Waived
                                       
                                       
                                   870.2400
                                Eye irritation
                                    Slight
                                      III
                                   00138094
                                   870.2500
                               Dermal irritation
                                    Slight
                                      III
                                   00074304
                                   870.2600
                             Dermal sensitization
                                    Waived
                                       
                                       


Table 2.0. Acute Toxicological Values for Kinetin
                                   Guideline
                                     Study
                                    Results
                                   Category
                                    MRID #
                                   870.1100
                               Acute Oral (rat)
                             LD50 > 5,000mg/kg
                                      IV
                                   45500703
                                   870.1200
                                 Acute Dermal
                             LD50 > 5,000 mg/kg
                                      IV
                                   45500704
                                   870.1300
                               Acute Inhalation
                              LC50 > 2.09 mg/L
                                      IV
                                   45500705
                                   870.2400
                                Eye irritation
                                     mild
                                      III
                                   45500706
                                   870.2500
                               Dermal irritation
                                Non-irritating
                                      IV
                                   45500707
                                   870.2600
                             Dermal sensitization
                           Not a contact sensitizer
                                       
                                   45500708

Only the four naturally occurring cytokinins, derived from certain algal species, are exempt from the requirement of a tolerance when used as a plant growth regulator (40 CFR 180.1042). Tolerance exemptions are often based on the results of 90-Day (or longer) feeding and developmental toxicity studies submitted to support reregistration. However, it is the Agency's opinion that these studies can be waived for naturally occurring and synthetic cytokinin because of low acute mammalian toxicity and very low use rates (250 grams ai/A), which would not significantly increase dietary intake over natural consumption in foods. The Agency, will be proposing an exemption from the requirement of a tolerance for certain cytokinins (zeatin [6-(4-hydroxy-3-methylbut-trans-2-enylamino)-purine], N6-methylaminopurine, N6-dimethylamino purine, N6- isopentenyl- aminopurine), and synthetic cytokinin -- kinetin [6- (furfurylamino) purine] for all raw agricultural commodities (RACs). The exemption will apply only when application rates do not exceed 250 grams of active ingredient/acre/year. The Agency believes this action does not present any unreasonable risk. It is based on cytokinin's low acute mammalian toxicity, its low use rates, exposure in the diet from numerous natural plant food sources, and minimal exposure in the diet derived from consumption of treated commodities under the proposed maximum label use rates. The Agency has concluded that dietary exposure risks from consuming commodities treated with cytokinin, either naturally occurring or synthetic, are not expected.

Ecotoxicity
Ecological toxicity studies on non-target terrestrial and aquatic organisms were waived because available information shows that cytokinin does not cause unreasonable adverse effects: 1) The principal constituents of cytokinin, algae and seaweed, are natural components of fish diets; 2) Cytokinin has a very low acute mammalian toxicity; 3) Cytokinin is used as a dietary supplement in animal feeds; 4) are expected to have no adverse effects to fish and wildlife; and 5) no reported incidents. Data waivers were also granted for Nontarget Insect Testing (885.4340) and Nontarget Plant Testing (885.4300) in July of 1995 as part of the RED development process because of the unique characteristics of this product, its non-toxic mode of action, low use volumes (< 2g/A), and biodegradability (low to no persistence). Based on the current use patterns, the non-toxic effects to terrestrial and aquatic plants and animals, the Agency finds that Cytokinin use is a No Effect to endangered plant and animal species from current registered uses. 





References

Arteca, R. (1996). Plant Growth Substances: Principles and Applications. New York: Chapman & Hall. 
Mauseth, J. D. (1991). Botany: An Introduction to Plant Biology. Philadelphia: Saunders. pp. 348-415.
Raven, P. H., Evert, R. F., and Eichhorn, S. E. (1992). Biology of Plants. New York: Worth. pp. 545-572.
Salisbury, F. B., and Ross, C. W. (1992). Plant Physiology. Belmont, CA: Wadsworth. pp. 357-407, 531-548.
USEPA 738-R-95-025 Environmental Protection And Toxic Substances December 1995 Agency (7508W) Reregistration Eligibility Decision (RED).






