UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, DC 20460

			OFFICE OF  PREVENTION, PESTICIDES,  AND TOXIC SUBSTANCES

 

MEMORANDUM								July 11, 2007

Subject: 	Environmental Fate Risk Assessment of Zinc Naphthenate for the
Reregistration Eligibility Decision (RED) 

To:		Tim McMahon, PhD., Risk Assessor and Senior Toxicologist

		Antimicrobials Division (7510P)

				And

Kathryn Jakob, CRM for Zinc Naphthenate RED

		Regulatory Management Branch II

		Antimicrobials Division (7510P)

From:		A. Najm Shamim. PhD, Chemist

		Regulatory Management Branch II

		Antimicrobials Division (7510P)

Thru:		Diane Isbell, Team Leader

		Regulatory Management Branch II

		Antimicrobials Division (7510P)

			And

		Mark Hartman, Chief

		Regulatory Management Branch II

		Antimicrobials Division (7510P)

EXECUTIVE SUMMARY:

Zinc Naphthenate is an antimicrobial pesticide registered for use as a
wood preservative and fungicide.  No environmental fate data were
submitted by registrants for a risk assessment. The only data submitted
for zinc naphthenate was a leaching study with southern pine surface and
pressure treated wood.  No open literature data for zinc naphthenate
exist for environmental fate parameters. The Agency has decided to
bridge the fate data of copper naphthenate for zinc naphthenate. It
should be noted that for copper naphthenate, only some environmental
fate parameters are known through modeling estimations.

Zinc naphthenate, like copper naphthenate is a likely to be stable
substance in water under aerobic and abiotic conditions, with an
estimated half life of more than three months1 and it  is  likely to be
highly to moderately immobile in soils with an estimated Koc of over
30001. It is not highly water soluble and has a low vapor pressure (~
10-4 mm Hg) and air/water partition coefficient (estimated Henry Law
Constant) for copper naphthenate is ~ 9.804x 10-6 and therefore   zinc
naphthenate like copper naphthenate is likely to evaporate from water
surfaces to a high degree as well as it is likely to contaminate surface
water by way of soil run-offs.  Zinc naphthenate like copper naphthenate
is likely to persist in water and soils.

Estimated log Kow for zinc naphthenate is possibly similar to that of
copper naphthenate which is 4.1685 1.  This would indicate that zinc
naphthenate can possibly be bioaccumulative in aquatic organisms like
fish.  Estimated half life of copper naphthenate in air is 8.858 hours 
and zinc naphthenate may likely to have a similar value  and is not
likely to be persistent in air.

A laboratory study2 on southern yellow pine stakes has shown that zinc
naphthenate does leach from the surface and pressure treated wood.  The
rates of leaching from the surface and pressure treated follow the
order:  rate of leaching is highest in pH 5>> pH 7 > unbuffered solution
> pH 9.  The rate of leaching from surface treated wood at pH 5 is:
0.112 ppm/cm2 /day and for pH 9 it is 0. 0026, ppm/cm2 /day a 40- -fold
less.  Similarly the rate of leaching from a pressure treated wood at pH
5 is: 0.019 ppm/cm2 / day and for pH 9 the value is 0.0012, a rate of
leaching is 16-fold less. Because of a high Koc zinc naphthenate is
likely to contaminate surface soils around the treated wood.

APPENDIX FOR ENVIRONMENTAL FATE ASSESSMENT OF ZINC NAPHTHENATE

Southern yellow pine stakes were treated with zinc naphthenate with the
following regiment:

Type of Treatment		Zinc Retention (lbs/ft3)

	Pressure			Mean: 0.08, Max: 0.12, min: 0.06

	Surface			Mean: 0.08, max: 0.20; min: 0.01

The Study author points out that the a typical pressure treatment target
level  for commercial use is 0.08 lbs/ft3  as set by AWPA’s Standard
C4-93.

The exposed area of the treated wood has been estimated by the
registrants as follows: wood dimensions: 1.5 x 1.5 x 3.0 inches.

[ 4 sides x 1.5 x 3.0 inches] + [ 2 ends x 1.5 x 1.5 inches] – [1 end
x 1.5 x 1.5 inches] = 20.3 in2 

14) Because of the low solubility of zinc naphthenate in water, emulsion
solutions were prepared using organic solvents.

The study showed:

Order of leaching: pH  5>> pH 7 > unbuffered > pH 9

At the end of 30 day period of the study  total zinc leachate were
determined by using the following relationship: total zinc leached
(ppm/in2 ) = total zinc leached (ppm) / exposed surface area (in2 )

Agency calculated the total zinc leach in ppm/in2 and converted them
into ppm/cm2 and then calculated the rate (ppm/cm2/day) as shown below.

SUMMARY OF THE LEACHING DATA FOR SURFACE TREATED WOOD OF ZINC
NAPHTHENATE

					Table 1

Matrix+	t 

0 hr	t

1 hr	t

1 d	T

7 d	t

14 d	T

21 d	t

30

d	Total

Ppm	ppm

/20.3in2	ppm/

cm2	Rate=

ppm/ cm2 /30d

pH 5	ND*	7.5	33.1	69.47	82.0	87.98	92.19	372.23	18.33	5.45	0.112

pH 7	ND*	3.31	23.46	46.93	50.51	52.01	53.45	229.67	11.31	2.07	0.069

pH 9	ND*	0.16	0.87	1.55	1.92	2.15	2.28	8.93	0.43	0.078	0.0026

Unbuff.	ND*	4.78	26.46	48.69	52.04	52.52	51.52	236.01	11.67	2.14	0.071



Notes: 1) * not detected; below detection limit

2) + means samples in deionized water and buffered. Unbuffered means
deionized water which is not buffered.

	SUMMARY OF THE LEACHING DATA FOR PRESSURE TREATED WOOD OF ZINC
NAPHTHENATE

						Table 2

Matrix + 	t=

0 hr	t=

1 hr	t =

1 d	t=

7d	T=

 

14 d	t=

21d	t=

30d 	Total ppm	ppm /  20.3 in2	ppm/ cm2	Rate = ppm/

m2/d

pH 5	ND*	1.06	4.52	10.49	14.02	16.35	18.39	64.83	3.19	0.585	0.019

pH 7

	ND*	0.72	2.39	4.16	4.86	5.22	5.45	22.82	1.12	0.20	0.006

pH 9

	ND*	ND*	03.5	0.77	0.93	1.0	1.04	4.09	0.20	0.036	0.0012

Un-buff	ND*	1.28	4.7	9.63	12.42	14.71	15.87	58.66	2.88	0.530	0.017



Notes:  1) * means not detected; below detection limit

2) + means samples in deionized water and buffered. Unbuffered means
deionized water which is not buffered.

Bibliography

US EPA document MRID#: 440951-01:

Zinc Naphthenate Leachability From Treated Wood, A Non-Guideline Study
for the AD Fate  Data Requirements  1996, by A.C. Gallacher. Dept. of
Analytical Services, Ricerca, Inc. 7528 Auburn Rd.; PO Box 1000,
Painesville, Ohio, 44077-1000

Cc:  Chemfile (Case 3099), RMBII, Najm Shamim

