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Terrestrial safety assessment of linear alkylbenzene sulfonate
Chemosphere, Vol.21, Nos.l-2, Printed in Great Britain
pp
251-262,
TERRESTRIAL SAFETY A S S ~
J. P. Mieure*,
1990
0045-6535/90 $3.00 Pergamon Press plc
O F LINEAR ~ B ~ N Z ~ q E
J. Waters**, M. S. Holt***,
SUI/DNATE
and E. Matthijs****
*Monsanto Company, 800 North Lindbergh Blvd., St. Louis, MO 63167, U.S.A. (to whom all correspondence should be directed) **Unilever Research Ltd., Port Sunlight Laboratory, Wirral, U.K. ***Shell Research Ltd., Sittingbourne Research Center, U.K. ****Procter & Gamble, European Technical Center, Strombeck-Bever, Belgium
ABSTRACT
This paper presents a safety assessment for linear alkylbenzene sulfonate (LAS) to terrestrial plants and animals and includes results from recent published and unpublished studies. Comparisons of measured LAS concentrations in the soil environment with the lowest effect concentrations for typical terrestrial organisms demonstrate adequate margins of safety of i0-i00 for irrigation with sewage plant effluent and of 78-131 for fertilization with sewage sludge. INTRODUCTION
The anionic surfactant linear alkylbenzene sulfonate (LAS) is the principal surfactant in heavy duty household laundry detergents. Its safe use in detergents dates back approximately 25 years when its replacement of lessdegradable branched alkylbenzene sulfonate resulted in immediate improvement to the aquatic environment. The rapid and complete biodegradation of LAS has been well demonstrated (1,2). The toxicity to aquatic organisms has also been thoroughly characterized and acceptable margins of safety exist between effect levels and the very low levels of LAS found in surface waters (3,4). The environmental safety of LAS was recently the subject of a comprehensive critical literature review by Painter and Zabel (5). Although some studies on toxicity to plants have been published, no thorough assessment of the safety of LAS to terrestrial organisms has been conducted. The purpose of this paper is to present such an assessment.
251
+
.00
252
Two routes of p o t e n t i a l e x p o s u r e of t e r r e s t r i a l plants and a n i m a l s to LAS need to be c o n s i d e r e d in a risk assessment. A l t h o u g h LAS is r e a d i l y b i o d e g r a d e d d u r i n g sewage treatment, small amounts m a y be present in the a q u e o u s d i s c h a r g e f r o m a s e w a g e t r e a t m e n t plant. In r a r e circumstances, t h i s e f f l u e n t m a y be u s e d d i r e c t l y for crop irrigation, w h i c h w o u l d r e p r e s e n t one p o t e n t i a l e x p o s u r e scenario. (River w a t e r is m u c h m o r e likely to be u s e d for irrigation; the lower LAS c o n c e n t r a t i o n s in rivers lead to larger m a r g i n s of s a f e t y t h a n for effluents. This s c e n a r i o is not f o r m a l l y a s s e s s e d in this paper.) The second, and m o r e likely, e x p o s u r e s c e n a r i o is from the d i s p o s a l of sewage sludge on soil. The sludge from a sewage t r e a t m e n t plant t y p i c a l l y c o n t a i n s m e a s u r a b l e c o n c e n t r a t i o n s of LAS, t y p i c a l l y 0.3 - 1.2% on d r i e d solids (6,7,8). This sludge m a y be incinerated, p l a c e d in a landfill or p l a c e d o n or u n d e r the s u r f a c e of soil as a fertilizer. The safety of e x p o s u r e of t e r r e s t r i a l p l a n t s and animals to LAS from i r r i g a t i o n use of sewage e f f l u e n t and from f e r t i l i z e r use of sewage sludge is a s s e s s e d in this paper. METHODS
L a b o r a t o r y Studies M e t h o d s The m e t h o d s u s e d t o d e t e r m i n e the e n v i r o n m e n t a l fate, e f f e c t s and e x p o s u r e c o n c e n t r a t i o n s in t h e p u b l i s h e d studies u s e d for t h i s a s s e s s m e n t are r e p o r t e d in the r e s p e c t i v e publications. The reader is d i r e c t e d to t h o s e r e f e r e n c e s for f u r t h e r information. D e t a i l s are g i v e n here for four u n p u b l i s h e d studies. In the first study (9) the e f f e c t s of a c o m m e r c i a l LAS m i x t u r e h a v i n g 10-13 c a r b o n s in the alkyl chain, w i t h average chain length 11.6, w e r e i n v e s t i g a t e d on t h r e e plant species. The plants w e r e s o r g h u m (Sorqhum bicolor), s u n f l o w e r (Helianthus annuus) and m u n g b e a n (Phaseolus aureus). The p r o c e d u r e u s e d was d e s i g n e d t o m e e t O E C D requirements. (OECD. G u i d e l i n e for T e s t i n g of C h e m i c a l s No. 208. T e r r e s t r i a l Plants G r o w t h Test. 1984.) Plants w e r e g r o w n in a c o m m e r c i a l l y a v a i l a b l e p o t t i n g compost, WC-B, w h i c h was a m i x t u r e of grit, loam and slow release fertilizers. Non-porous plastic p l a n t pots i0 cm in d i a m e t e r and h o l d i n g a p p r o x i m a t e l y 600g of soil w e r e used. A n a q u e o u s s o l u t i o n of test m a t e r i a l was m i x e d w i t h silver sand, w h i c h was s u b s e q u e n t l y i n c o r p o r a t e d into the W C - B at 1:9 ratio to p r o d u c e the g r o w t h medium. C o n c e n t r a t i o n s t e s t e d (expressed as active ingredient) w e r e i000, 100, i0 and i m g / k g dry soil. E a c h pot was sown w i t h 8 seeds, w i t h four r e p l i c a t e pots per concentration. T e s t s w e r e c o n d u c t e d in a g r e e n h o u s e m a i n t a i n e d at a n o m i n a l t e m p e r a t u r e of 20°C w i t h a 14-hour d a y l i g h t i0 - hour d a r k cycle. The soil was kept m o i s t by t w i c e d a i l y watering. E m e r g e n c e was e v a l u a t e d after seven days w h i l e g r o w t h was m o n i t o r e d after 21 days.
253
The second study (i0) utilized experimental techniques designed as a general screen for herbicidal activity. These studies were designed to closely simulate the real world disposal of sludge on soil. The LAS was mixed with anaerobic sewage sludge (60-65% organic carbon on dry basis), then mixed thoroughly into unsterilized soil. In one set of experiments the seeds were planted in the soil the same day the LAS/sludge mixture was applied (treatment OWK). In another set the seeds were planted two weeks after application of the LAS/sludge mixture to determine any mitigation due to LAS biodegradation (treatment 2WK). Two different commercial LAS blends, typical of current U.S. production, were tested. These blends had average carbon chain lengths of 11.36 and 13.13 respectively, for the alkyl portion of the molecule. The test species were chosen to be representative of a broad spectrum of common plants and included five crop plants. The individual species were: Yellow nutsedge Barnyard grass Grain sorghum (Dekalb 59E) Wheat (Caldwell) Corn (Pioneer 3358) Soybean (Williams 82) Morningglory Cocklebur Velvetleaf
Cyperus esculentus L. Echinochloa crus-qalli Sorqhum bicolor Triticum vulaare Zea mays Giycine max Ipomoea purpurea Xanthium strumarium Abutilon theophrasti Medik
Sugarbeet was also included in the study, but very low germination in all dose levels and in controls prevented meaningful data interpretation. Each concentration was run in duplicate in unsterilized silt loam soil in bread pan containers. After dosing the pans were placed in a greenhouse, one replicate and one untreated control per bench. The greenhouse was operated on a 14 hour light i0 hour dark photoperiod at a temperature of 25-28°C. Each group of plants was observed 2 weeks after planting. All observations were by comparison to untreated controls. The LAS application rates ranged up to 407 and 392 ~g/g, respectively, for the 11.36 and 13.13 carbon chain length products. The sludge application rates for all treated samples corresponded to approximately 8000 pound per acre (9000 kg/hectare), which is high compared to typical application rates. The earthworm is the most widely tested invertebrate for estimating risk to soil-dwelling animals. Tests of LAS toxicity to two strains of earthworm have recently been completed. Both tests were conducted using a commercial LAS blend with average carbon chain length of 11.36 (typical of LAS chain lengths found in the environment), described above in the phytotoxicity screening section. The first study (ii) was conducted using Eisenia foetida and based on OECD guidelines. (OECD. Guideline for Testing of Chemicals No. 207. Earthworm Acute Toxicity Tests. 1984.) The adult test animals had an initial mean weight of 0.66 g per individual. The test soil was comprised of 70% 5010 grade silica sand, 20% kaolinite clay and 10% finely ground sphagnum peat. The constituents were blended in a concrete mixer. Appropriate weights of test material were mixed with water and added to the dry soil to produce soil with approximately 35% moisture.
254
Soil p o r t i o n s w e i g h i n g 900g w e r e p l a c e d into 32 o u n c e glass Jars. Ten e a r t h w o r m s w e r e a d d e d to each jar, w i t h four r e p l i c a t e s (40 worms) at e a c h test c o n c e n t r a t i o n (nominally i000, 500, 250, 125, 63 and 0 ~ g / g dry weight). Soil m o i s t u r e was m a i n t a i n e d at 35 ± 1% and t e m p e r a t u r e was m a i n t a i n e d at 20 ± 2°C. L i g h t i n g was 2 4 - h o u r c o n t i n u o u s at a p p r o x i m a t e l y 600 lux from cool w h i t e f l u o r e s c e n c e lamps. E a r t h w o r m s w e r e a s s e s s e d for mortality, g e n e r a l health, b o d y w e i g h t and b e h a v i o r after 7 and 14 days. The s e c o n d e a r t h w o r m study (12) was c o n d u c t e d u s i n g L u m b r i c u s t e r r e s t r i s b a s e d on U.S. F o o d and Drug A d m i n i s t r a t i o n guidelines. (U.S. Food and D r u g A d m i n i s t r a t i o n . E a r t h w o r m S u b a c u t e Toxicity. F D A E n v i r o n m e n t a l A s s e s s m e n t T e c h n i c a l G u i d e No. 4.12. March, 1987.) The adult test animals had an initial m e a n w e i g h t of 3.2 g per individual. The test soil was c o m p r i s e d of 70% s i l i c a sand, 20% k a o l i n i t e c l a y and 10% s p h a g n u m peat. R a b b i t feces was a d d e d as food at 50g/kg (dry/basis). All c o n s t i t u e n t s w e r e b l e n d e d in a c o n c r e t e mixer. A p p r o p r i a t e w e i g h t s of LAS w e r e d i s s o l v e d in d e i o n i z e d w a t e r and added to dry soil to p r o d u c e soil w i t h 25% moisture. Soil p o r t i o n s w e i g h i n g 900g w e r e p l a c e d in one g a l l o n g l a s s jars. Ten w o r m s w e r e a d d e d t o e a c h jar, w i t h four r e p l i c a t e s (40 worms) at e a c h test c o n c e n t r a t i o n (nominally 1333, 667, 333, 167, 84 and 0 ~ g / g dry weight). Soil m o i s t u r e w a s m a i n t a i n e d at 25-29% and t e m p e r a t u r e was m a i n t a i n e d at 13 ± 2°C. L i g h t i n g w a s 24 hours c o n t i n u o u s at 700-750 lux from cool w h i t e f l u o r e s c e n c e lamps. E a r t h w o r m s w e r e a s s e s s e d for mortality, general health, b o d y w e i g h t and b e h a v i o r after 7 and 14 days. SAFETY
ASSESSMENT
METHOD
The s a f e t y a s s e s s m e n t for t h e s e t e r r e s t r i a l data on LAS was c o n d u c t e d u s i n g the same p r i n c i p l e s as apply to aquatic risk a s s e s s m e n t (3,4). P u b l i s h e d and u n p u b l i s h e d d a t a from t e s t s for adverse e f f e c t s on r e p r e s e n t a t i v e p l a n t s and animals w e r e u s e d to e s t a b l i s h the r a n g e of harmful effect c o n c e n t r a t i o n s . P u b l i s h e d LAS c o n c e n t r a t i o n s in w a s t e w a t e r and in soil w e r e u s e d to d e t e r m i n e the r a n g e of exposures. M a r g i n s of safety w e r e o b t a i n e d by c o m p a r i n g the c o n c e n t r a t i o n s c a u s i n g a d v e r s e e f f e c t s w i t h the e x p o s u r e c o n c e n t r a t i o n s . When r e s u l t s from s i m i l a r tests on e f f e c t s w e r e available, r e s u l t s from the t e s t s m o s t c l o s e l y s i m u l a t i n g real e n v i r o n m e n t a l e x p o s u r e w e r e u s e d for the assessment.
255
RESULTS
AND
DISCUSSION
Use of Sewaqe Plant Effluent for Irriuation I.
Effects on terrestrial plants. Results from nine studies where water containing LAS was used to irrigate plants have been published and are summarized in Table I. A total of eleven plant species were tested. In general when toxicity or growth inhibition was observed, it was in the range of i0 to i000 mg/l. The most sensitive species were orchids and vegetables grown hydroponically (radish, Chinese cabbage and rice), and the lowest reported adverse effect level was i0 mg/l. TABLE I Effects of LAS on Terrestrial Plants by Irrigation
Species
Results
References
Peas
Growth inhibited at 50 mg/l
13
Orchids
Growth inhibited at I0 and i00 mg/l
14
Paddy Rice
Production inhibited at 50 mg/l
15
Potted Rice
Yellowing of leaf blade at 50 mg/l
15
Barley; Beans, Tomato
No effect at 40 mg/l Stimulated growth at 25 and 40 mg/l
16
Norfolk Island Pine
Reduced growth at i00 mg/l
17
Radish, Chinese Cabbage & Rice in Hydroponics
10 mg/l is "critical" concentration
18
Rice Seedlings
5 mg/l promoted growth, 40 mg/l inhibited growth
19
Barley, Radish, Pea, Tomato, Lettuce
Retarded growth at 1000 mg/l, no effect at 100 mg/l
20
Cucumber
Retarded growth at i00 mg/l, no effect at 10 mg/l.
20
256
If.
E f f e c t s on t e r r e s t r i a l animals. Few s t a n d a r d i z e d tests have b e e n d e v e l o p e d for e s t a b l i s h i n g t o x i c i t y of c h e m i c a l s to t e r r e s t r i a l animals in a g r i c u l t u r a l soils. P r o b a b l y the o n l y s i g n i f i c a n t tests m e e t i n g this r e q u i r e m e n t use t h e earthworm. R e s u l t s of t e s t s d e s c r i b e d above on LAS w i t h two strains of earthworm, E i s e n i a foetida and L u m b r i c u s terrestris, are r e p o r t e d here. For E i s e n i a the 14-day LC 50 was g r e a t e r t h a n the m a x i m u m test c o n c e n t r a t i o n of i000 ~g/g. All groups had 100% survival e x c e p t the h i g h dose, w h i c h had 95% survival. A 33% and 23% r e d u c t i o n in b o d y w e i g h t was o b s e r v e d at i00 and 500 ~g/g, vs. a 14% r e d u c t i o n for the controls. Based on statistical a n a l y s i s of the w e i g h t data, the no effect c o n c e n t r a t i o n was the nominal 250 ~ g / g dose, w h i c h was c o n f i r m e d by H P L C to be 235 ~g/g. For L u m b r i c u s the 14-day LC 50 was g r e a t e r t h a n the m a x i m u m test c o n c e n t r a t i o n of 1333 ~g/g. M o r t a l i t y v a r i e d from 0 to 22.5%, but t h e r e w e r e no s t a t i s t i c a l l y significant d i f f e r e n c e s among t r e a t m e n t groups. B a s e d on w e i g h t and b u r r o w i n g behavior, the no effect c o n c e n t r a t i o n was t h e nominal 667 ~ g / g dose, m e a s u r e d b y HPLC to be 613 ~g/g. It is s i g n i f i c a n t t o note that b o t h of these e a r t h w o r m p r o t o c o l s u t i l i z e d a 2 4 - h o u r light/0 hour d a r k cycle. Thus the w o r m s w e r e forced t o r e m a i n in the soil and in contact w i t h the LAS. E s p e c i a l l y in the case of Lumbricus, the light p r e v e n t e d normal feeding, w h i c h is a c c o m p l i s h e d at night on the surface. Thus t h e s e test c o n d i t i o n s are m o r e severe t h a n likely to be e n c o u n t e r e d in real w o r l d e x p o s u r e s at c o m p a r a b l e concentrations.
III.
Concentrations
in w a t e r used for irrigation.
In d e v e l o p e d c o u n t r i e s most d o m e s t i c w a s t e w a t e r is s u b j e c t e d to b i o l o g i c a l treatment. It has b e e n r e p o r t e d that LAS c o n c e n t r a t i o n s in sewage t r e a t m e n t p l a n t e f f l u e n t are g e n e r a l l y in the 0 . 0 2 - 0 . 9 m g / l c o n c e n t r a t i o n range (2,6). In regions w h e r e w a t e r is scarce, w a s t e w a t e r m a y be u s e d for c r o p irrigation. For a c t i v a t e d sludge t r e a t m e n t plants the LAS e f f l u e n t c o n c e n t r a t i o n s in the U.S., Canada, S w i t z e r l a n d and West G e r m a n y w e r e r e p o r t e d to a v e r a g e 0.05, 0.09, 0.09 and 0.07 mg/l, r e s p e c t i v e l y (2). A e r a t e d lagoon, o x i d a t i o n d i t c h and r o t a t i n g b i o l o g i c a l c o n t a c t o r e f f l u e n t c o n c e n t r a t i o n s are in the same range (21). T r i c k l i n g filter p l a n t s are t y p i c a l l y less e f f i c i e n t at r e m o v i n g o r g a n i c c h e m i c a l constituents, and e f f l u e n t c o n c e n t r a t i o n s may reach 0.9 mg/l (2). Thus c r o p i r r i g a t i o n u s i n g t r i c k l i n g filter plant e f f l u e n t r e p r e s e n t s the h i g h e s t e x p o s u r e a n t i c i p a t e d in a p r a c t i c a l sense.
257
IV.
R i s k a s s e s s m e n t for irrigation. F r o m the above d i s c u s s i o n the most s e n s i t i v e of t h i r t e e n t e s t e d t e r r e s t r i a l p l a n t and animal species were e f f e c t e d at levels of I0 mg/l LAS in i r r i g a t i o n water. C o n c e n t r a t i o n s of LAS in the e f f l u e n t from the most c o m m o n l y u s e d types of s e c o n d a r y sewage t r e a t m e n t c o n t a i n an a v e r a g e of 0.09 mg/l. E f f l u e n t from t r i c k l i n g filter p l a n t s r e p r e s e n t the w o r s t case LAS c o n c e n t r a t i o n s of 0.9 m g / l from b i o l o g i c a l treatment. C o m p a r i n g the effect c o n c e n t r a t i o n t o the c o n c e n t r a t i o n s r e s u l t i n g from this r a n g e of b i o l o g i c a l t r e a t m e n t leads to a d e q u a t e m a r g i n s of safety in the I0-i00 range.
Use of S e w a q e Plant Sludqe for F e r t i l i z e r I.
E f f e c t s on t e r r e s t r i a l plants P h y t o t o x i c i t y studies d e s c r i b e d p r e v i o u s l y (Table I) w e r e c o n d u c t e d b y a d d i n g LAS via i r r i g a t i o n water. Two recent s t u d i e s d e s c r i b e d in the M e t h o d s s e c t i o n u s e d a d o s i n g r e g i m e n r e l e v a n t to the a p p l i c a t i o n of sludge to soil. R e s u l t s from t h e s e studies are r e p o r t e d here. For the first study, results of the tests for s u n f l o w e r i n d i c a t e d over 91% e m e r g e n c e in all t r e a t e d soils. For m u n g b e a n e m e r g e n c e was over 84% for I,i0 and i00 ~g/g, and 75% at i000 ~g/g. For s o r g h u m b e t w e e n 78 and 64% of the seeds e m e r g e d in control, i,i0 and i00 ~g/g, and 69% e m e r g e d at I000 ~g/g. T h e r e f o r e the 7-day EC 50 for e m e r g e n c e is g r e a t e r t h a n I000 ~ g / g for all 3 species. The 2 1 - d a y E C 50 c o n c e n t r a t i o n s for g r o w t h w e r e 289 ~ g / g for sunflower, 316 ~ g / g for m u n g b e a n and 167 ~ g / g for sorghum. The h i g h e s t n o - e f f e c t c o n c e n t r a t i o n was i00 ~ g / g for e a c h species. For the second study, the L A S / s l u d g e a p p l i c a t i o n g e n e r a l l y r e s u l t e d in p r o m o t i o n r a t h e r than r e t a r d a t i o n of plant growth. T h e r e f o r e the results of this test are s u m m a r i z e d in terms of promotion. Growth p r o m o t i o n for individual species ranged b e t w e e n -5 and 55% across the c o n c e n t r a t i o n r a n g e studied. The g r o w t h p r o m o t i o n r e s p o n s e was g r e a t e r for n a r r o w l e a f t h a n for b r o a d l e a f species. T a b l e II shows the p e r c e n t g r o w t h p r o m o t i o n a v e r a g e d over all species for e a c h p l a n t i n g time and a p p l i c a t i o n rate. Individual data are shown in T a b l e III for the C11.36 c h a i n length LAS, w h i c h is t y p i c a l of h o m o l o g d i s t r i b u t i o n s found in the environment. The g r o w t h p r o m o t i o n w i t h i n e a c h species w a s v i r t u a l l y c o n s t a n t for all LAS c o n c e n t r a t i o n s in the set w h e r e seed p l a n t i n g was d e l a y e d two weeks. G r o w t h p r o m o t i o n d e c r e a s e d at h i g h e r LAS c o n c e n t r a t i o n s in the set w h e r e seeds w e r e p l a n t e d on the same day as LAS treatment. This is of no p r a c t i c a l significance, since the normal p r a c t i c e is to a p p l y sludge several w e e k s b e f o r e p l a n t i n g crops. In summary, t h e r e was no s i g n i f i c a n t effect on seed g e r m i n a t i o n and no s i g n i f i c a n t g r o w t h i n h i b i t i o n on nine p l a n t species at LAS c o n c e n t r a t i o n s u p to 407 Bg/g dry soil.
258
TABLE II Average Percent Growth Promotion
from LAS Spiked Sludge
C11.~Chain Lenqth Concentration (~g/g)
C13.13Chain Lenqth Planting Time OWK
407.0 238.3 154.0 111.8 90.7 69.6*
Concentration (~g/g)
Planting Time
2WK
1 4 12 21 20 16
OWK
20 22 27 17 28 19
391.9 231.1 150.4 110.0 89.8 69.6*
* The sludge used for this study contributed ~g/g C12.6 LAS to the soil.
i0 9 12 11 18 16
the equivalent
2WK 15 17 14 22 17 19
of 69.6
TABLE III Individual
Percent Growth Promotion
Species
Yellow Nutsedge Barnyard Grass Grain Sorghum Wheat Corn Soybean Morningglory Cocklebur Velvetleaf
Avg.
from C11.36 LAS Spiked Sludge
Concentration (~g/g) 111.8 15__~4 283.3
0t
69.6*
90.7
40___/7
0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0
15,10# 25,40 15,25 20,5 15,15 5,10 5,20 20,5 20,40
15,25 30,55 15,40 15,20 25,30 15,15 25,25 20,0 20,40
15,10 30,40 20,35 20,5 25,10 10,5 10,20 30,5 30,25
15,25 25,50 20,35 20,5 10,10 5,5 10,20 0,5 5,25
5,10 10,40 0,30 0,15 10,15 0,10 5,30 0,10 5,35
0,25 0,55 5,40 5,0 0,20 0,5 0,10 -5,0 0,25
0,0
16,19
20,28
21,17
12,17
4,22
1,20
Contained neither sludge nor LAS. # For each pair of results, the first value is the growth promotion when seeds were planted the same day the sludge and LAS were added; the second value is the growth promotion when seeds were planted two weeks after adding sludge and LAS.
259
II.
Concentrations in Sludge Amended Soil At least four groups of researchers have recently studied the concentrations and fate of LAS in sludge amended soil in real world situations. Berna et al. (8) studied LAS concentrations in grapevine and vegetable soils fertilized with sludge from Spanish sewage treatment plants. LAS concentrations ir~mediately after sludge addition ranged from 16.4 to 52.5 ~g/g soil. The concentration dropped steadily during the observation period, with half lives ranging from 26 to 33 days. Giger et al. (7) studied LAS concentrations in an experimental plot in Switzerland which had received high doses of sludge for I0 previous years. These workers found an initial LAS soil concentration of approximately 45 ~g/g immediately after adding sludge. The LAS decreased very rapidly over the first ten days, with a half llfe of about 5 days. De Henau (6) reported that four amended soils from Europe ranged from 0.9 - 2.2 ~g/g. By far the most comprehensive study of LAS in sludge amended soil was reported by Waters et al (22,23). This study encompassed 51 fields on 24 farms in the Thames Water Authority region of southern England sampled in 1987. The sites provided a range of soil types; sludge compositions and origins; frequency, levels and types of sludge applications and agricultural uses (pasture/arable). Forty-two sites which had received their most recent sludge application prior to 1987 were found to contain soil LAS levels in the 0 - 2.5 ~g/g range (83% contained less than 1 ~g/g). Nine sites which had received sludge in 1987 prior to the May sampling were found to have soil LAS concentrations in the 0.2 - 19.8 ~g/g range. In addition five fields were monitored in a time course experiment to determine disappearance rates. The initial concentrations in the fields ranged from 2.6 to 66.4 ~g/g, the later value resulting from sampling directly in the furrow following subsurface injection. LAS half-lives for these five fields were calculated to be between 7 and 22 days.
III.
Risk Assessment for Sludge Amended Soil Phytotoxicity tests described above were conducted in the presence and absence of sludge and the effect concentrations agreed within approximately a factor of two. Since LAS predominantly enters the soil environment adsorbed on sludge, the results from the tests with sludge are the most environmentally relevant and were used for this assessment. The lowest no adverse effect concentration of 392 ~g/g for a species was used in the current assessment. For terrestrial animals the 14-day no effect concentrations were 235 and 613 ~g/g, respectively for Eisenia and Lumbricus. The lowest value, 235 ~g/g, was chosen for this assessment.
260
M e a s u r e m e n t s of LAS in sludge a m e n d e d soil w e r e s u m m a r i z e d a b o v e for 63 sites r e p r e s e n t i n g a w i d e v a r i e t y of sludge a p p l i c a t i o n s and soil types. T h e s e studies can be c h a r a c t e r i z e d into two categories; o n e - t i m e s a m p l i n g to m e a s u r e p o t e n t i a l e x p o s u r e from p r e v i o u s a p p l i c a t i o n s and m u l t i p l e s a m p l i n g over time, b e g i n n i n g i m m e d i a t e l y after application, to m e a s u r e w o r s t case, short t e r m c o n c e n t r a t i o n s and d i s a p p e a r a n c e rates. R e s u l t s from 46 sites fit the first c a t e g o r y and are u s e f u l for a s s e s s i n g long t e r m risk to t e r r e s t r i a l plants and animals. LAS c o n c e n t r a t i o n s at 37 of t h o s e 46 sites w e r e less t h a n or e q u a l to 1.0 ~g/g; c o n c e n t r a t i o n s at the other 9 sites were all less t h a n 3 ~g/g. T h e r e f o r e 3 ~ g / g can be used as a r e a l i s t i c u p p e r b o u n d for long t e r m e x p o s u r e in sludge a m e n d e d soil. C o m p a r i n g the c o n c e n t r a t i o n s c a u s i n g adverse e f f e c t s t o t e r r e s t r i a l a n i m a l s and p l a n t s (235 and 392 ~g/g) w i t h the h i g h e s t c o n c e n t r a t i o n from the long t e r m m o n i t o r i n g data (< 3 ~g/g) gives m a r g i n s of safety of g r e a t e r than 78 and 131, respectively. T h e s e m a r g i n s are m o r e t h a n a d e q u a t e to p r o t e c t t e r r e s t r i a l plants and animals. R e s u l t s from the s h o r t - t e r m d i s a p p e a r a n c e rate studies show that initial LAS soil c o n c e n t r a t i o n s i m m e d i a t e l y after adding sludge to soil r a n g e from 2.6 to 66.4 ~ g / g (the latter v a l u e from s a m p l i n g d i r e c t l y in the furrow i m m e d i a t e l y after s u b s u r f a c e sludge injection). The soil d i s a p p e a r a n c e half lives from t w e l v e m e a s u r e m e n t s r a n g e d from 5 to 33 days, w i t h a m e d i a n of 15.2 days. Since crops are not t y p i c a l l y p l a n t e d u n t i l at least a m o n t h after soil is a m e n d e d w i t h sludge, a p p r o x i m a t e l y two half lives can be a s s u m e d to t r a n s p i r e b e f o r e seeds are sown. Thus soil c o n c e n t r a t i o n s can be e x p e c t e d to d e c l i n e to less t h a n one fourth t h e initial c o n c e n t r a t i o n b e f o r e seeds or new t r a n s p l a n t s are exposed. A p p l y i n g this m o d e l to the e x i s t i n g d a t a b a s e gives a m a r g i n of safety of 23 for c r o p plants u s i n g the highest LAS c o n c e n t r a t i o n o b s e r v e d in 17 soils. Conclusion. The m a r g i n s of safety d e r i v e d above appear m o r e t h a n a d e q u a t e to p r o t e c t t e r r e s t r i a l plants and animals from h a r m by LAS d u r i n g i r r i g a t i o n w i t h s e c o n d a r y sewage e l e m e n t or u p o n soil f e r t i l i z a t i o n w i t h sewage sludge. The a s s e s s m e n t was b a s e d on t o x i c i t y test results from 22 t e r r e s t r i a l p l a n t species and two strains of t e r r e s t r i a l invertebrate, and on m o r e t h a n i00 m e a s u r e m e n t s of LAS c o n c e n t r a t i o n s in the environment. This is s u f f i c i e n t i n f o r m a t i o n to p r o v i d e a high degree of statistical c o n f i d e n c e in the assessment. ACKNOWLEDGEMENTS
The authors are d e e p l y i n d e b t e d to L i n d a Thomas and F u m i o Y o s h i k a w a of M o n s a n t o for c o n d u c t i n g p h y t o t o x i c i t y screening tests, to D o n a l d V e r s t e e g of P r o c t e r and Gamble, J o s e p h G o r s u c h of E a s t m a n K o d a k and J a m e s S w i g e r t of ABC L a b o r a t o r i e s for useful d i s c u s s i o n s on e a r t h w o r m testing, to R i c h a r d K i m e r l e and W i l l i a m G l e d h i l l of M o n s a n t o for e d i t o r i a l advice and to K a r l a U n d e r w o o d and Janet S u s a n g for p r e p a r i n g this manuscript.
261
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CITED
1.
R. D. Swisher, Surfactant Biodegradation, Second Edition, Marcel Dekker, Inc., New York (1987) Chapter 6.II pp. 424-457.
2.
H.A.
3.
W. F. Holman and K. J. Macek, Transactions of the American Fisheries Society 109, 122 (1980).
4.
R.A.
5.
H. A. Painter and T. F. Zabel, Review of the Environmental Impact of LAS, WRC Report CO 1659-M/EV 8658, Medmenham Laboratory, Henley Road, Medmenham, P.O. Box 16, Marlow, Bucks, SL7 2HD, England.
6.
H. de Henau, E. Matthijs and W. D. Hopping, 26, 279 (1986).
7.
W. Giger, A. C. Alder, P. H. Brunner, A. Marcomini and H. Siegrist, Tenside 26, 95 (1989).
8.
J. L. Berna, J. Ferrer, A. Moreno, D. Prats and F. R. Bevia, Tenside 26, i01 (1989).
9.
Unilever, "Effects on the Growth of Sorqhum Bicolor, Helianthus Annuus and Phaseolus Aureus", contract study conducted for Unilever Research Port Sunlight Laboratory, UK, by ICI, Brixham Laboratory, UK. Study Report BL/B/3078, August 1987.
10.
L. Thomas and F. Yoshikawa, Effects of Sludge and Planting Time on the Herbicidal Activity of Linear Alkylbenzene Sulfonates, Monsanto Company report H88-21-4, 1988.
Ii.
Monsanto, "Acute Toxicity of (Eisenia foetida)", contract Company, St. Louis, Missouri, Laboratories, Inc., Columbia, 1990.
12.
Monsanto, "Acute Toxicity of Linear Alkylbenzene Sulfonate to Earthworms (Lumbricus terrastris)", contract study conducted for Monsanto Chemical Company, St. Louis, Missouri, USA, by Analytical Bio-Chemistry Laboratories, Inc., Columbia, Missouri, USA, report 38317, February 1990.
13.
E . P . Lichtenstein, T. W. Fuhremann, N.E.A. Scopes and R. F. Skrentry, J. Agr. Food Chem. 15, 864 (1967).
14.
R. Ernst, J. Arditti,
15.
T. Taniyama, Mie Daigaku Kankyo Kagaku Kenkyu Kinyo 3, 93 (1978).
Painter and T. Zabel, Tenside 26, 108 (1989).
Kimerle,
Tenside 26, 169 (1989).
Int. J. Environ. Anal. Chem.
Linear Alkylbenzene Sulfonate to Earthworms study conducted for Monsanto Chemical USA, by Analytical Bio-Chemistry Missouri, USA, report 38316, February,
and P. L. Healy, New Phytol. 70, 457 (1971).
262
REFERENCES CITED (continued) 16.
A. Lopez-Zavala, A. S. deAluja, B. Elias, L. Maujarrez, A. B. Buchmann, L. Mercado and S. Caltenco, Prog. Water Technol. ~, 73 (1975).
17.
H.G.M. Dowden, M. J. Lambert and R. Trum, Aust. J. Plant Physiol. 5, 387 (1979).
18.
Y. Takita, Yukagaku 31, 507 (1982).
19.
N. Wakiuchi, M. Yokoyama, Y. Oji and S. Okamoto, Kobe Daigaku Nogakubu Kenkyu Hokoku 12, 128 (1988).
20.
P.A.
Gilbert and H. H. Kleiser, Tenside 25, 128 (1988).
21.
R.A.
Rapaport,
22.
J. Waters, M. S. Holt and E. Matthijs, Tenside 26, 129 (1989).
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M.S.
(Received
Procter & Gamble, private communication.
Holt, E. Matthijs and J. Waters, Water Research 23, 749 (1989).
in
USA
22
April
1990;
accepted
ii J u n e
1990)
pp
251-262,
TERRESTRIAL SAFETY A S S ~
J. P. Mieure*,
1990
0045-6535/90 $3.00 Pergamon Press plc
O F LINEAR ~ B ~ N Z ~ q E
J. Waters**, M. S. Holt***,
SUI/DNATE
and E. Matthijs****
*Monsanto Company, 800 North Lindbergh Blvd., St. Louis, MO 63167, U.S.A. (to whom all correspondence should be directed) **Unilever Research Ltd., Port Sunlight Laboratory, Wirral, U.K. ***Shell Research Ltd., Sittingbourne Research Center, U.K. ****Procter & Gamble, European Technical Center, Strombeck-Bever, Belgium
ABSTRACT
This paper presents a safety assessment for linear alkylbenzene sulfonate (LAS) to terrestrial plants and animals and includes results from recent published and unpublished studies. Comparisons of measured LAS concentrations in the soil environment with the lowest effect concentrations for typical terrestrial organisms demonstrate adequate margins of safety of i0-i00 for irrigation with sewage plant effluent and of 78-131 for fertilization with sewage sludge. INTRODUCTION
The anionic surfactant linear alkylbenzene sulfonate (LAS) is the principal surfactant in heavy duty household laundry detergents. Its safe use in detergents dates back approximately 25 years when its replacement of lessdegradable branched alkylbenzene sulfonate resulted in immediate improvement to the aquatic environment. The rapid and complete biodegradation of LAS has been well demonstrated (1,2). The toxicity to aquatic organisms has also been thoroughly characterized and acceptable margins of safety exist between effect levels and the very low levels of LAS found in surface waters (3,4). The environmental safety of LAS was recently the subject of a comprehensive critical literature review by Painter and Zabel (5). Although some studies on toxicity to plants have been published, no thorough assessment of the safety of LAS to terrestrial organisms has been conducted. The purpose of this paper is to present such an assessment.
251
+
.00
252
Two routes of p o t e n t i a l e x p o s u r e of t e r r e s t r i a l plants and a n i m a l s to LAS need to be c o n s i d e r e d in a risk assessment. A l t h o u g h LAS is r e a d i l y b i o d e g r a d e d d u r i n g sewage treatment, small amounts m a y be present in the a q u e o u s d i s c h a r g e f r o m a s e w a g e t r e a t m e n t plant. In r a r e circumstances, t h i s e f f l u e n t m a y be u s e d d i r e c t l y for crop irrigation, w h i c h w o u l d r e p r e s e n t one p o t e n t i a l e x p o s u r e scenario. (River w a t e r is m u c h m o r e likely to be u s e d for irrigation; the lower LAS c o n c e n t r a t i o n s in rivers lead to larger m a r g i n s of s a f e t y t h a n for effluents. This s c e n a r i o is not f o r m a l l y a s s e s s e d in this paper.) The second, and m o r e likely, e x p o s u r e s c e n a r i o is from the d i s p o s a l of sewage sludge on soil. The sludge from a sewage t r e a t m e n t plant t y p i c a l l y c o n t a i n s m e a s u r a b l e c o n c e n t r a t i o n s of LAS, t y p i c a l l y 0.3 - 1.2% on d r i e d solids (6,7,8). This sludge m a y be incinerated, p l a c e d in a landfill or p l a c e d o n or u n d e r the s u r f a c e of soil as a fertilizer. The safety of e x p o s u r e of t e r r e s t r i a l p l a n t s and animals to LAS from i r r i g a t i o n use of sewage e f f l u e n t and from f e r t i l i z e r use of sewage sludge is a s s e s s e d in this paper. METHODS
L a b o r a t o r y Studies M e t h o d s The m e t h o d s u s e d t o d e t e r m i n e the e n v i r o n m e n t a l fate, e f f e c t s and e x p o s u r e c o n c e n t r a t i o n s in t h e p u b l i s h e d studies u s e d for t h i s a s s e s s m e n t are r e p o r t e d in the r e s p e c t i v e publications. The reader is d i r e c t e d to t h o s e r e f e r e n c e s for f u r t h e r information. D e t a i l s are g i v e n here for four u n p u b l i s h e d studies. In the first study (9) the e f f e c t s of a c o m m e r c i a l LAS m i x t u r e h a v i n g 10-13 c a r b o n s in the alkyl chain, w i t h average chain length 11.6, w e r e i n v e s t i g a t e d on t h r e e plant species. The plants w e r e s o r g h u m (Sorqhum bicolor), s u n f l o w e r (Helianthus annuus) and m u n g b e a n (Phaseolus aureus). The p r o c e d u r e u s e d was d e s i g n e d t o m e e t O E C D requirements. (OECD. G u i d e l i n e for T e s t i n g of C h e m i c a l s No. 208. T e r r e s t r i a l Plants G r o w t h Test. 1984.) Plants w e r e g r o w n in a c o m m e r c i a l l y a v a i l a b l e p o t t i n g compost, WC-B, w h i c h was a m i x t u r e of grit, loam and slow release fertilizers. Non-porous plastic p l a n t pots i0 cm in d i a m e t e r and h o l d i n g a p p r o x i m a t e l y 600g of soil w e r e used. A n a q u e o u s s o l u t i o n of test m a t e r i a l was m i x e d w i t h silver sand, w h i c h was s u b s e q u e n t l y i n c o r p o r a t e d into the W C - B at 1:9 ratio to p r o d u c e the g r o w t h medium. C o n c e n t r a t i o n s t e s t e d (expressed as active ingredient) w e r e i000, 100, i0 and i m g / k g dry soil. E a c h pot was sown w i t h 8 seeds, w i t h four r e p l i c a t e pots per concentration. T e s t s w e r e c o n d u c t e d in a g r e e n h o u s e m a i n t a i n e d at a n o m i n a l t e m p e r a t u r e of 20°C w i t h a 14-hour d a y l i g h t i0 - hour d a r k cycle. The soil was kept m o i s t by t w i c e d a i l y watering. E m e r g e n c e was e v a l u a t e d after seven days w h i l e g r o w t h was m o n i t o r e d after 21 days.
253
The second study (i0) utilized experimental techniques designed as a general screen for herbicidal activity. These studies were designed to closely simulate the real world disposal of sludge on soil. The LAS was mixed with anaerobic sewage sludge (60-65% organic carbon on dry basis), then mixed thoroughly into unsterilized soil. In one set of experiments the seeds were planted in the soil the same day the LAS/sludge mixture was applied (treatment OWK). In another set the seeds were planted two weeks after application of the LAS/sludge mixture to determine any mitigation due to LAS biodegradation (treatment 2WK). Two different commercial LAS blends, typical of current U.S. production, were tested. These blends had average carbon chain lengths of 11.36 and 13.13 respectively, for the alkyl portion of the molecule. The test species were chosen to be representative of a broad spectrum of common plants and included five crop plants. The individual species were: Yellow nutsedge Barnyard grass Grain sorghum (Dekalb 59E) Wheat (Caldwell) Corn (Pioneer 3358) Soybean (Williams 82) Morningglory Cocklebur Velvetleaf
Cyperus esculentus L. Echinochloa crus-qalli Sorqhum bicolor Triticum vulaare Zea mays Giycine max Ipomoea purpurea Xanthium strumarium Abutilon theophrasti Medik
Sugarbeet was also included in the study, but very low germination in all dose levels and in controls prevented meaningful data interpretation. Each concentration was run in duplicate in unsterilized silt loam soil in bread pan containers. After dosing the pans were placed in a greenhouse, one replicate and one untreated control per bench. The greenhouse was operated on a 14 hour light i0 hour dark photoperiod at a temperature of 25-28°C. Each group of plants was observed 2 weeks after planting. All observations were by comparison to untreated controls. The LAS application rates ranged up to 407 and 392 ~g/g, respectively, for the 11.36 and 13.13 carbon chain length products. The sludge application rates for all treated samples corresponded to approximately 8000 pound per acre (9000 kg/hectare), which is high compared to typical application rates. The earthworm is the most widely tested invertebrate for estimating risk to soil-dwelling animals. Tests of LAS toxicity to two strains of earthworm have recently been completed. Both tests were conducted using a commercial LAS blend with average carbon chain length of 11.36 (typical of LAS chain lengths found in the environment), described above in the phytotoxicity screening section. The first study (ii) was conducted using Eisenia foetida and based on OECD guidelines. (OECD. Guideline for Testing of Chemicals No. 207. Earthworm Acute Toxicity Tests. 1984.) The adult test animals had an initial mean weight of 0.66 g per individual. The test soil was comprised of 70% 5010 grade silica sand, 20% kaolinite clay and 10% finely ground sphagnum peat. The constituents were blended in a concrete mixer. Appropriate weights of test material were mixed with water and added to the dry soil to produce soil with approximately 35% moisture.
254
Soil p o r t i o n s w e i g h i n g 900g w e r e p l a c e d into 32 o u n c e glass Jars. Ten e a r t h w o r m s w e r e a d d e d to each jar, w i t h four r e p l i c a t e s (40 worms) at e a c h test c o n c e n t r a t i o n (nominally i000, 500, 250, 125, 63 and 0 ~ g / g dry weight). Soil m o i s t u r e was m a i n t a i n e d at 35 ± 1% and t e m p e r a t u r e was m a i n t a i n e d at 20 ± 2°C. L i g h t i n g was 2 4 - h o u r c o n t i n u o u s at a p p r o x i m a t e l y 600 lux from cool w h i t e f l u o r e s c e n c e lamps. E a r t h w o r m s w e r e a s s e s s e d for mortality, g e n e r a l health, b o d y w e i g h t and b e h a v i o r after 7 and 14 days. The s e c o n d e a r t h w o r m study (12) was c o n d u c t e d u s i n g L u m b r i c u s t e r r e s t r i s b a s e d on U.S. F o o d and Drug A d m i n i s t r a t i o n guidelines. (U.S. Food and D r u g A d m i n i s t r a t i o n . E a r t h w o r m S u b a c u t e Toxicity. F D A E n v i r o n m e n t a l A s s e s s m e n t T e c h n i c a l G u i d e No. 4.12. March, 1987.) The adult test animals had an initial m e a n w e i g h t of 3.2 g per individual. The test soil was c o m p r i s e d of 70% s i l i c a sand, 20% k a o l i n i t e c l a y and 10% s p h a g n u m peat. R a b b i t feces was a d d e d as food at 50g/kg (dry/basis). All c o n s t i t u e n t s w e r e b l e n d e d in a c o n c r e t e mixer. A p p r o p r i a t e w e i g h t s of LAS w e r e d i s s o l v e d in d e i o n i z e d w a t e r and added to dry soil to p r o d u c e soil w i t h 25% moisture. Soil p o r t i o n s w e i g h i n g 900g w e r e p l a c e d in one g a l l o n g l a s s jars. Ten w o r m s w e r e a d d e d t o e a c h jar, w i t h four r e p l i c a t e s (40 worms) at e a c h test c o n c e n t r a t i o n (nominally 1333, 667, 333, 167, 84 and 0 ~ g / g dry weight). Soil m o i s t u r e w a s m a i n t a i n e d at 25-29% and t e m p e r a t u r e was m a i n t a i n e d at 13 ± 2°C. L i g h t i n g w a s 24 hours c o n t i n u o u s at 700-750 lux from cool w h i t e f l u o r e s c e n c e lamps. E a r t h w o r m s w e r e a s s e s s e d for mortality, general health, b o d y w e i g h t and b e h a v i o r after 7 and 14 days. SAFETY
ASSESSMENT
METHOD
The s a f e t y a s s e s s m e n t for t h e s e t e r r e s t r i a l data on LAS was c o n d u c t e d u s i n g the same p r i n c i p l e s as apply to aquatic risk a s s e s s m e n t (3,4). P u b l i s h e d and u n p u b l i s h e d d a t a from t e s t s for adverse e f f e c t s on r e p r e s e n t a t i v e p l a n t s and animals w e r e u s e d to e s t a b l i s h the r a n g e of harmful effect c o n c e n t r a t i o n s . P u b l i s h e d LAS c o n c e n t r a t i o n s in w a s t e w a t e r and in soil w e r e u s e d to d e t e r m i n e the r a n g e of exposures. M a r g i n s of safety w e r e o b t a i n e d by c o m p a r i n g the c o n c e n t r a t i o n s c a u s i n g a d v e r s e e f f e c t s w i t h the e x p o s u r e c o n c e n t r a t i o n s . When r e s u l t s from s i m i l a r tests on e f f e c t s w e r e available, r e s u l t s from the t e s t s m o s t c l o s e l y s i m u l a t i n g real e n v i r o n m e n t a l e x p o s u r e w e r e u s e d for the assessment.
255
RESULTS
AND
DISCUSSION
Use of Sewaqe Plant Effluent for Irriuation I.
Effects on terrestrial plants. Results from nine studies where water containing LAS was used to irrigate plants have been published and are summarized in Table I. A total of eleven plant species were tested. In general when toxicity or growth inhibition was observed, it was in the range of i0 to i000 mg/l. The most sensitive species were orchids and vegetables grown hydroponically (radish, Chinese cabbage and rice), and the lowest reported adverse effect level was i0 mg/l. TABLE I Effects of LAS on Terrestrial Plants by Irrigation
Species
Results
References
Peas
Growth inhibited at 50 mg/l
13
Orchids
Growth inhibited at I0 and i00 mg/l
14
Paddy Rice
Production inhibited at 50 mg/l
15
Potted Rice
Yellowing of leaf blade at 50 mg/l
15
Barley; Beans, Tomato
No effect at 40 mg/l Stimulated growth at 25 and 40 mg/l
16
Norfolk Island Pine
Reduced growth at i00 mg/l
17
Radish, Chinese Cabbage & Rice in Hydroponics
10 mg/l is "critical" concentration
18
Rice Seedlings
5 mg/l promoted growth, 40 mg/l inhibited growth
19
Barley, Radish, Pea, Tomato, Lettuce
Retarded growth at 1000 mg/l, no effect at 100 mg/l
20
Cucumber
Retarded growth at i00 mg/l, no effect at 10 mg/l.
20
256
If.
E f f e c t s on t e r r e s t r i a l animals. Few s t a n d a r d i z e d tests have b e e n d e v e l o p e d for e s t a b l i s h i n g t o x i c i t y of c h e m i c a l s to t e r r e s t r i a l animals in a g r i c u l t u r a l soils. P r o b a b l y the o n l y s i g n i f i c a n t tests m e e t i n g this r e q u i r e m e n t use t h e earthworm. R e s u l t s of t e s t s d e s c r i b e d above on LAS w i t h two strains of earthworm, E i s e n i a foetida and L u m b r i c u s terrestris, are r e p o r t e d here. For E i s e n i a the 14-day LC 50 was g r e a t e r t h a n the m a x i m u m test c o n c e n t r a t i o n of i000 ~g/g. All groups had 100% survival e x c e p t the h i g h dose, w h i c h had 95% survival. A 33% and 23% r e d u c t i o n in b o d y w e i g h t was o b s e r v e d at i00 and 500 ~g/g, vs. a 14% r e d u c t i o n for the controls. Based on statistical a n a l y s i s of the w e i g h t data, the no effect c o n c e n t r a t i o n was the nominal 250 ~ g / g dose, w h i c h was c o n f i r m e d by H P L C to be 235 ~g/g. For L u m b r i c u s the 14-day LC 50 was g r e a t e r t h a n the m a x i m u m test c o n c e n t r a t i o n of 1333 ~g/g. M o r t a l i t y v a r i e d from 0 to 22.5%, but t h e r e w e r e no s t a t i s t i c a l l y significant d i f f e r e n c e s among t r e a t m e n t groups. B a s e d on w e i g h t and b u r r o w i n g behavior, the no effect c o n c e n t r a t i o n was t h e nominal 667 ~ g / g dose, m e a s u r e d b y HPLC to be 613 ~g/g. It is s i g n i f i c a n t t o note that b o t h of these e a r t h w o r m p r o t o c o l s u t i l i z e d a 2 4 - h o u r light/0 hour d a r k cycle. Thus the w o r m s w e r e forced t o r e m a i n in the soil and in contact w i t h the LAS. E s p e c i a l l y in the case of Lumbricus, the light p r e v e n t e d normal feeding, w h i c h is a c c o m p l i s h e d at night on the surface. Thus t h e s e test c o n d i t i o n s are m o r e severe t h a n likely to be e n c o u n t e r e d in real w o r l d e x p o s u r e s at c o m p a r a b l e concentrations.
III.
Concentrations
in w a t e r used for irrigation.
In d e v e l o p e d c o u n t r i e s most d o m e s t i c w a s t e w a t e r is s u b j e c t e d to b i o l o g i c a l treatment. It has b e e n r e p o r t e d that LAS c o n c e n t r a t i o n s in sewage t r e a t m e n t p l a n t e f f l u e n t are g e n e r a l l y in the 0 . 0 2 - 0 . 9 m g / l c o n c e n t r a t i o n range (2,6). In regions w h e r e w a t e r is scarce, w a s t e w a t e r m a y be u s e d for c r o p irrigation. For a c t i v a t e d sludge t r e a t m e n t plants the LAS e f f l u e n t c o n c e n t r a t i o n s in the U.S., Canada, S w i t z e r l a n d and West G e r m a n y w e r e r e p o r t e d to a v e r a g e 0.05, 0.09, 0.09 and 0.07 mg/l, r e s p e c t i v e l y (2). A e r a t e d lagoon, o x i d a t i o n d i t c h and r o t a t i n g b i o l o g i c a l c o n t a c t o r e f f l u e n t c o n c e n t r a t i o n s are in the same range (21). T r i c k l i n g filter p l a n t s are t y p i c a l l y less e f f i c i e n t at r e m o v i n g o r g a n i c c h e m i c a l constituents, and e f f l u e n t c o n c e n t r a t i o n s may reach 0.9 mg/l (2). Thus c r o p i r r i g a t i o n u s i n g t r i c k l i n g filter plant e f f l u e n t r e p r e s e n t s the h i g h e s t e x p o s u r e a n t i c i p a t e d in a p r a c t i c a l sense.
257
IV.
R i s k a s s e s s m e n t for irrigation. F r o m the above d i s c u s s i o n the most s e n s i t i v e of t h i r t e e n t e s t e d t e r r e s t r i a l p l a n t and animal species were e f f e c t e d at levels of I0 mg/l LAS in i r r i g a t i o n water. C o n c e n t r a t i o n s of LAS in the e f f l u e n t from the most c o m m o n l y u s e d types of s e c o n d a r y sewage t r e a t m e n t c o n t a i n an a v e r a g e of 0.09 mg/l. E f f l u e n t from t r i c k l i n g filter p l a n t s r e p r e s e n t the w o r s t case LAS c o n c e n t r a t i o n s of 0.9 m g / l from b i o l o g i c a l treatment. C o m p a r i n g the effect c o n c e n t r a t i o n t o the c o n c e n t r a t i o n s r e s u l t i n g from this r a n g e of b i o l o g i c a l t r e a t m e n t leads to a d e q u a t e m a r g i n s of safety in the I0-i00 range.
Use of S e w a q e Plant Sludqe for F e r t i l i z e r I.
E f f e c t s on t e r r e s t r i a l plants P h y t o t o x i c i t y studies d e s c r i b e d p r e v i o u s l y (Table I) w e r e c o n d u c t e d b y a d d i n g LAS via i r r i g a t i o n water. Two recent s t u d i e s d e s c r i b e d in the M e t h o d s s e c t i o n u s e d a d o s i n g r e g i m e n r e l e v a n t to the a p p l i c a t i o n of sludge to soil. R e s u l t s from t h e s e studies are r e p o r t e d here. For the first study, results of the tests for s u n f l o w e r i n d i c a t e d over 91% e m e r g e n c e in all t r e a t e d soils. For m u n g b e a n e m e r g e n c e was over 84% for I,i0 and i00 ~g/g, and 75% at i000 ~g/g. For s o r g h u m b e t w e e n 78 and 64% of the seeds e m e r g e d in control, i,i0 and i00 ~g/g, and 69% e m e r g e d at I000 ~g/g. T h e r e f o r e the 7-day EC 50 for e m e r g e n c e is g r e a t e r t h a n I000 ~ g / g for all 3 species. The 2 1 - d a y E C 50 c o n c e n t r a t i o n s for g r o w t h w e r e 289 ~ g / g for sunflower, 316 ~ g / g for m u n g b e a n and 167 ~ g / g for sorghum. The h i g h e s t n o - e f f e c t c o n c e n t r a t i o n was i00 ~ g / g for e a c h species. For the second study, the L A S / s l u d g e a p p l i c a t i o n g e n e r a l l y r e s u l t e d in p r o m o t i o n r a t h e r than r e t a r d a t i o n of plant growth. T h e r e f o r e the results of this test are s u m m a r i z e d in terms of promotion. Growth p r o m o t i o n for individual species ranged b e t w e e n -5 and 55% across the c o n c e n t r a t i o n r a n g e studied. The g r o w t h p r o m o t i o n r e s p o n s e was g r e a t e r for n a r r o w l e a f t h a n for b r o a d l e a f species. T a b l e II shows the p e r c e n t g r o w t h p r o m o t i o n a v e r a g e d over all species for e a c h p l a n t i n g time and a p p l i c a t i o n rate. Individual data are shown in T a b l e III for the C11.36 c h a i n length LAS, w h i c h is t y p i c a l of h o m o l o g d i s t r i b u t i o n s found in the environment. The g r o w t h p r o m o t i o n w i t h i n e a c h species w a s v i r t u a l l y c o n s t a n t for all LAS c o n c e n t r a t i o n s in the set w h e r e seed p l a n t i n g was d e l a y e d two weeks. G r o w t h p r o m o t i o n d e c r e a s e d at h i g h e r LAS c o n c e n t r a t i o n s in the set w h e r e seeds w e r e p l a n t e d on the same day as LAS treatment. This is of no p r a c t i c a l significance, since the normal p r a c t i c e is to a p p l y sludge several w e e k s b e f o r e p l a n t i n g crops. In summary, t h e r e was no s i g n i f i c a n t effect on seed g e r m i n a t i o n and no s i g n i f i c a n t g r o w t h i n h i b i t i o n on nine p l a n t species at LAS c o n c e n t r a t i o n s u p to 407 Bg/g dry soil.
258
TABLE II Average Percent Growth Promotion
from LAS Spiked Sludge
C11.~Chain Lenqth Concentration (~g/g)
C13.13Chain Lenqth Planting Time OWK
407.0 238.3 154.0 111.8 90.7 69.6*
Concentration (~g/g)
Planting Time
2WK
1 4 12 21 20 16
OWK
20 22 27 17 28 19
391.9 231.1 150.4 110.0 89.8 69.6*
* The sludge used for this study contributed ~g/g C12.6 LAS to the soil.
i0 9 12 11 18 16
the equivalent
2WK 15 17 14 22 17 19
of 69.6
TABLE III Individual
Percent Growth Promotion
Species
Yellow Nutsedge Barnyard Grass Grain Sorghum Wheat Corn Soybean Morningglory Cocklebur Velvetleaf
Avg.
from C11.36 LAS Spiked Sludge
Concentration (~g/g) 111.8 15__~4 283.3
0t
69.6*
90.7
40___/7
0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0
15,10# 25,40 15,25 20,5 15,15 5,10 5,20 20,5 20,40
15,25 30,55 15,40 15,20 25,30 15,15 25,25 20,0 20,40
15,10 30,40 20,35 20,5 25,10 10,5 10,20 30,5 30,25
15,25 25,50 20,35 20,5 10,10 5,5 10,20 0,5 5,25
5,10 10,40 0,30 0,15 10,15 0,10 5,30 0,10 5,35
0,25 0,55 5,40 5,0 0,20 0,5 0,10 -5,0 0,25
0,0
16,19
20,28
21,17
12,17
4,22
1,20
Contained neither sludge nor LAS. # For each pair of results, the first value is the growth promotion when seeds were planted the same day the sludge and LAS were added; the second value is the growth promotion when seeds were planted two weeks after adding sludge and LAS.
259
II.
Concentrations in Sludge Amended Soil At least four groups of researchers have recently studied the concentrations and fate of LAS in sludge amended soil in real world situations. Berna et al. (8) studied LAS concentrations in grapevine and vegetable soils fertilized with sludge from Spanish sewage treatment plants. LAS concentrations ir~mediately after sludge addition ranged from 16.4 to 52.5 ~g/g soil. The concentration dropped steadily during the observation period, with half lives ranging from 26 to 33 days. Giger et al. (7) studied LAS concentrations in an experimental plot in Switzerland which had received high doses of sludge for I0 previous years. These workers found an initial LAS soil concentration of approximately 45 ~g/g immediately after adding sludge. The LAS decreased very rapidly over the first ten days, with a half llfe of about 5 days. De Henau (6) reported that four amended soils from Europe ranged from 0.9 - 2.2 ~g/g. By far the most comprehensive study of LAS in sludge amended soil was reported by Waters et al (22,23). This study encompassed 51 fields on 24 farms in the Thames Water Authority region of southern England sampled in 1987. The sites provided a range of soil types; sludge compositions and origins; frequency, levels and types of sludge applications and agricultural uses (pasture/arable). Forty-two sites which had received their most recent sludge application prior to 1987 were found to contain soil LAS levels in the 0 - 2.5 ~g/g range (83% contained less than 1 ~g/g). Nine sites which had received sludge in 1987 prior to the May sampling were found to have soil LAS concentrations in the 0.2 - 19.8 ~g/g range. In addition five fields were monitored in a time course experiment to determine disappearance rates. The initial concentrations in the fields ranged from 2.6 to 66.4 ~g/g, the later value resulting from sampling directly in the furrow following subsurface injection. LAS half-lives for these five fields were calculated to be between 7 and 22 days.
III.
Risk Assessment for Sludge Amended Soil Phytotoxicity tests described above were conducted in the presence and absence of sludge and the effect concentrations agreed within approximately a factor of two. Since LAS predominantly enters the soil environment adsorbed on sludge, the results from the tests with sludge are the most environmentally relevant and were used for this assessment. The lowest no adverse effect concentration of 392 ~g/g for a species was used in the current assessment. For terrestrial animals the 14-day no effect concentrations were 235 and 613 ~g/g, respectively for Eisenia and Lumbricus. The lowest value, 235 ~g/g, was chosen for this assessment.
260
M e a s u r e m e n t s of LAS in sludge a m e n d e d soil w e r e s u m m a r i z e d a b o v e for 63 sites r e p r e s e n t i n g a w i d e v a r i e t y of sludge a p p l i c a t i o n s and soil types. T h e s e studies can be c h a r a c t e r i z e d into two categories; o n e - t i m e s a m p l i n g to m e a s u r e p o t e n t i a l e x p o s u r e from p r e v i o u s a p p l i c a t i o n s and m u l t i p l e s a m p l i n g over time, b e g i n n i n g i m m e d i a t e l y after application, to m e a s u r e w o r s t case, short t e r m c o n c e n t r a t i o n s and d i s a p p e a r a n c e rates. R e s u l t s from 46 sites fit the first c a t e g o r y and are u s e f u l for a s s e s s i n g long t e r m risk to t e r r e s t r i a l plants and animals. LAS c o n c e n t r a t i o n s at 37 of t h o s e 46 sites w e r e less t h a n or e q u a l to 1.0 ~g/g; c o n c e n t r a t i o n s at the other 9 sites were all less t h a n 3 ~g/g. T h e r e f o r e 3 ~ g / g can be used as a r e a l i s t i c u p p e r b o u n d for long t e r m e x p o s u r e in sludge a m e n d e d soil. C o m p a r i n g the c o n c e n t r a t i o n s c a u s i n g adverse e f f e c t s t o t e r r e s t r i a l a n i m a l s and p l a n t s (235 and 392 ~g/g) w i t h the h i g h e s t c o n c e n t r a t i o n from the long t e r m m o n i t o r i n g data (< 3 ~g/g) gives m a r g i n s of safety of g r e a t e r than 78 and 131, respectively. T h e s e m a r g i n s are m o r e t h a n a d e q u a t e to p r o t e c t t e r r e s t r i a l plants and animals. R e s u l t s from the s h o r t - t e r m d i s a p p e a r a n c e rate studies show that initial LAS soil c o n c e n t r a t i o n s i m m e d i a t e l y after adding sludge to soil r a n g e from 2.6 to 66.4 ~ g / g (the latter v a l u e from s a m p l i n g d i r e c t l y in the furrow i m m e d i a t e l y after s u b s u r f a c e sludge injection). The soil d i s a p p e a r a n c e half lives from t w e l v e m e a s u r e m e n t s r a n g e d from 5 to 33 days, w i t h a m e d i a n of 15.2 days. Since crops are not t y p i c a l l y p l a n t e d u n t i l at least a m o n t h after soil is a m e n d e d w i t h sludge, a p p r o x i m a t e l y two half lives can be a s s u m e d to t r a n s p i r e b e f o r e seeds are sown. Thus soil c o n c e n t r a t i o n s can be e x p e c t e d to d e c l i n e to less t h a n one fourth t h e initial c o n c e n t r a t i o n b e f o r e seeds or new t r a n s p l a n t s are exposed. A p p l y i n g this m o d e l to the e x i s t i n g d a t a b a s e gives a m a r g i n of safety of 23 for c r o p plants u s i n g the highest LAS c o n c e n t r a t i o n o b s e r v e d in 17 soils. Conclusion. The m a r g i n s of safety d e r i v e d above appear m o r e t h a n a d e q u a t e to p r o t e c t t e r r e s t r i a l plants and animals from h a r m by LAS d u r i n g i r r i g a t i o n w i t h s e c o n d a r y sewage e l e m e n t or u p o n soil f e r t i l i z a t i o n w i t h sewage sludge. The a s s e s s m e n t was b a s e d on t o x i c i t y test results from 22 t e r r e s t r i a l p l a n t species and two strains of t e r r e s t r i a l invertebrate, and on m o r e t h a n i00 m e a s u r e m e n t s of LAS c o n c e n t r a t i o n s in the environment. This is s u f f i c i e n t i n f o r m a t i o n to p r o v i d e a high degree of statistical c o n f i d e n c e in the assessment. ACKNOWLEDGEMENTS
The authors are d e e p l y i n d e b t e d to L i n d a Thomas and F u m i o Y o s h i k a w a of M o n s a n t o for c o n d u c t i n g p h y t o t o x i c i t y screening tests, to D o n a l d V e r s t e e g of P r o c t e r and Gamble, J o s e p h G o r s u c h of E a s t m a n K o d a k and J a m e s S w i g e r t of ABC L a b o r a t o r i e s for useful d i s c u s s i o n s on e a r t h w o r m testing, to R i c h a r d K i m e r l e and W i l l i a m G l e d h i l l of M o n s a n t o for e d i t o r i a l advice and to K a r l a U n d e r w o o d and Janet S u s a n g for p r e p a r i n g this manuscript.
261
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in
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accepted
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