The Pesticide Chemist and Modern Toxicology - ACS Publications

21 The Increased Role of Chemistry in Toxicology

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THOMAS CAIRNS Department of Health and Human Services, Food and Drug Administration, National Center for Toxicological Research, Jefferson, A R 72079

In this century society has by its proliferation of synthetic organic and inorganic chemicals including pesticides and herbicides given birth to a whole host of new interdisciplinary sciences. Toxicology has obviously been a product of this evolutionary process and is continuing to be a complex martrix of many basic sciences neatly and somewhat conveniently blended with the skill and creativity of a gourmet chef in the presentation of a great classic and outstanding dish for immediate consumption and praise. Indeed, i t is perhaps presumptuous for a humble chemist to attempt to delineate his particular professional role in this new technological development. The myriad of sub-specialities that are the building blocks of modern toxicology have largely contributed to a lack of understanding of a clear definition of the exact science of toxicology. Nevertheless the strengths of modern toxicology must be considered a direct synergistic result of the various component disciplines from which its comprises. Fundamental to modern toxicology is the role that analytical chemistry can play and has honestly derived from various quantum leaps in instrumental technologies through a continuing process of aggressive pioneership by the profession i t s e l f and related disciplines. In reflection, developments in capabilities have somehow managed to be in a kind of synchronous step with solving evolving problems that those enhanced capabilities have introduced to society. Chemical technology has greatly advanced our standard of living with concurrent threats to the health of society. In particular, further generations must be fully protected by a rational policy on chemical utilization. It is interesting to ponder the question: "Was i t growing knowledge of modern toxicology that compelled a re-examination of public policy regarding human exposure to toxic substances, or was i t increased public concern that forced science into greater participation?".

0097-6156/8l/0160-0335$05.00/0 © 1981 American Chemical Society

Bandal et al.; The Pesticide Chemist and Modern Toxicology ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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Experiments i n which suspect carcinogens are administered to animals i n massive q u a n t i t i e s over r e l a t i v e l y short p e r i o d s o f time have been challenged on s c i e n t i f i c grounds and are confusing and o f t e n d i s t r u s t e d by laymen who m y o p i c a l l y can only see the d i f f e r e n c e s between the experimental process and r e a l l i f e . It i s true to say that the "800 cans o f d i e t soda" perception has been a s e r i o u s impediment to the c r e d i b i l i t y o f modern t o x i c o l o g y and the r e s u l t a n t r e g u l a t o r y processes. There can be no doubt that i n the environment and i n c e r t a i n occupational s i t u a t i o n s , there are chemical agents which can increase the l i k e l i h o o d or t h r e a t o f human cancer. As an a n a l y t i c a l chemist f o r t u i t o u s l y transposed to oversee the s c i e n t i f i c and a d m i n i s t r a t i v e d i r e c t i o n o f the National Center f o r Toxicology Research (NCTR) f o r the l a s t two and one h a l f years I consider I have had more than ample time to soak up the essences of modern t o x i c o l o g y and break that b a r r i e r of presumptiveness as a chemist to d i s c u s s a u t h o r i t a t i v e l y the demanding r o l e that chemistry c o n t r i b u t e s to modern t o x i c o l o g y by i l l u s t r a t i n g a few selected examples from experiences at NCTR and then advancing f u t u r e trends and ideas o f c u r r e n t research t o p i c s .

N o n c l i n i c a l L a b o r a t o r i e s S t u d i e s - Good Laboratory P r a o t i o e s At the present time, three p r i n c i p l e sources o f evidence e x i s t for the i d e n t i f i c a t i o n and removal o f a chemical substance that might pose a c a r c i n o g e n i c t h r e a t to p u b l i c h e a l t h : 1. Epidemiologic evidence from exposed human populations; 2. Long-term chronic bioassays from animal s t u d i e s ; 3. S h o r t - t e r m or o t h e r t e s t s t h a t s u g g e s t c a r c i n o g e n i c activity. Of these three o p t i o n s , a p r o p e r l y conducted long-term chronic bioassay has been accepted as the d e f i n i t i v e model f o r e s t i m a t i n g the c a r c i n o g e n i c r i s k f o r humans. Having mammalian tumori n d u c t i o n as i t s end-point, the c h r o n i c bioassay i s the only source of d i r e c t evidence (other than i n humans) of c h e m i c a l l y induced tumors i n the mammalian s p e c i e s . Of a l l t e s t systems i t comes the c l o s e s t to mimicking human routes o f exposure and metabolic/pharmacological processes which a c t i v a t e and d i s t r i b u t e chemicals. In t e s t i n g f o r c a r c i n o g e n i c i t y v i a such a c h r o n i c bioassay p r o t o c o l , the i m p l i c a t i o n s on chemistry placed by the recent FDA r e g u l a t i o n s , "Good Laboratory P r a c t i c e " , can be summarized as follows 1. I d e n t i t y , p u r i t y , chemical p r o p e r t i e s and s t a b i l i t y o f the t e s t substance. 2. Handling and storage o f the t e s t substance. 3. A n a l y s i s o f the bioassay s u p p l i e s f o r e s s e n t i a l and/or deleterious ingredients.


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4.

Homogeneity, s t a b i l i t y and proper c o n c e n t r a t i o n o f the t e s t substance i n the dosage form. 5. S a f e t y s u r v e i l l a n c e o f personnel and work areas. 6. Safe disposal o f the chemical and contaminated experimental m a t e r i a l s . Obviously, the i n t e g r i t y o f a long-term study i s t h e r e f o r e h i g h l y dependent upon a number o f the above f a c t o r s . For i n s t a n c e , the compound 2-acetylaminofluorene (2-AAF) was a known model carcinogen selected f o r a 33-month study at NCTR i n v o l v i n g 24,192 female BALC/c mice fed 30, 35, 45, 60, 75, 100 and 150 ppm plus a c o n t r o l ( 1 ) . I n i t i a l l y , the f i r s t 10kg batch o f 2-AAF acquired was 85-90% pure and hence was p u r i f i e d i n house to the desired l e v e l . However, a l a t e r shipment o f 2-AAF r e c e i v e d assayed a t 16.2% pure. Had t h i s s i n g l e f a c t gone undetected the e n t i r e i n v e s t m e n t i n t h e e x p e r i m e n t m i g h t have r e s u l t e d i n erroneous data being reported. Test substances are u s u a l l y administered to the animals i n e i t h e r d i e t or the d r i n k i n g water. For very obvious c o s t e f f e c t i v e reasons ( b o t h manpower and c h o i c e o f method o f a n a l y s i s ) , the d r i n k i n g water i s the p r e f e r r e d route i f the t e s t compound i s both s o l u b l e and s t a b l e enough. A good example can be i l l u s t r a t e d from the s t a b i l i t y s t u d i e s on 4-aminobiphenyl a t pH7 and pH2 (Table I ) . Table I.

Stability of Aqueous Solutions of 4-Aminobiphenyl.HCI

Sampling intervals, days

1.0 p p m

0 1 2 4 8 16

0.989±0.003 0.973±0.012 0.968±0.005 0.976±0.021 0.950±0.001 0.936±0.002

a

b

c

Cone of 4-aminobiphenyl.HCI soins indicated b

100 p p m 98.9+0.35 99.2±0.42 97.9±0.90 98.6±1.0 98.3±0.31 98.9±0.50

b

1.0 p p m

c

1.01 ±0.001 0.781+0.001 0.649+0.019 0.459±0.020 0.365+0.023 0.282+0.011

3

100 ppm

c

93.8±0.00 79.3+0.02 73.5+0.17 60.4±2.3 62.4±0.66 57.4+1.1

M e a n and standard error from triplicate assays. A q u e o u s HCI solution (0.01Λ/, pH2), samples adjusted for control. Deionized water solution, samples adjusted for control.

With recent emphasis on conducting chronic bioassays sometimes at low c o n c e n t r a t i o n ranges o f the t e s t compound, the question o f t o x i c a n t and n u t r i e n t v a r i a b i l i t y o f commercial l a b o r a t o r y animal d i e t s has been e x t e n s i v e l y examined at NCTR over the l a s t f i v e years (2.,3.). The animal d i e t must be considered an important source o f v a r i a t i o n since the r e l a t i v e proportions and/or source


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of d i f f e r e n t i n g r e d i e n t s may w e l l v a r y d e p e n d i n g on the a v a i l a b i l i t y and cost o f raw m a t e r i a l s . Respecting t h i s p o s s i b l e v a r i a b i l i t y , commercial rodent feed has been analyzed at NCTR f o r the past f i v e years and the r e s u l t s of 148 l o t s are d i s p l a y e d i n Table II. As a n t i c i p a t e d , the variability of n u t r i e n t concentrations was much l e s s than that o f the trace p e s t i c i d e s found or the heavy m e t a l s . Using t h i s data base, the s p e c i f i c a t i o n l i m i t s i n d i c a t e d i n Table I I were s t r i c t l y adhered to and s e v e r a l three ton l o t s of feed had to be d i s c a r d e d . This type of survey has also provided the information to s e l e c t the s p e c i f i c a t i o n s based on what the market place could produce. In general, however, the annual average Cu and vitamin A concentrations were at l e a s t 12$ lower than the approximate concentrations l i s t e d by the manufacturer whereas Ca, p r o t e i n and vitamin Β were w i t h i n +5$ and f a t and Zn w i t h i n +8J of the manufacturer's s p e c i f i c a t i o n s . F r e q u e n t l y , Se was found a t concentration l e v e l s at which i t has been shown to i n t e r a c t with the p r o c e s s o f c h e m i c a l c a r c i n o g e n e s i s . Occasionally DDT,

TABLE Π.

The Twenty Parameters Used in Animal Feed Surveillance* Specification

Parameter

Aflatoxin, ppb (Bi, B2, d , G2) Lindane, ppb Heptachlor, ppb Malathion, ppm DDT (Total), ppb PCB, ppb Dieldrin, ppb Cadmium, ppb Arsenic, ppm Lead, ppm Mercury, ppb Selenium, ppm Calcium, % Copper, ppm Zinc, ppm Vitamin A, I.U./g Vitamin Bi, mg/100g Estrogenic activity, ppb Total Protein, g/100g Total Fat, g/100g

Std. Mean

L i m i t a t i o n

Min.

Max.

-

5

-

100 20 5 100 50 20 250 1.0 1.5 200 0.65

.05 0.75 8 75 15 7.5 21.0 4.3

-

*148 lots of Purina autoclavable Rodent Laboratory Chow 5010

Dev.

N.A.

-

75 12.5 5 23.0 6.7

1.67 1.07 0.33 27.72 8.7 2.4 87.3 0.31 0.47 0.024 0.34 1.16 15.0 108.2 41.6 9.1 5 24.2 5.54

analyzed prior to autoclaving.


3.6 2.2 0.52 48.4 15.1 4.6 33.2 0.18 0.38 0.02 0.15 0.18 2.8 9.7 36.9 1.25 N.A. 2.4 0.58

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d i e l d r i n , Cd and Pb were present c l o s e to the c o n c e n t r a t i o n l e v e l s known to have b i o l o g i c a l e f f e c t s . In t h i s monitoring program, animal s u p p l i e s were examined p r i o r to use to provide assurances that acceptable l e v e l s o f n u t r i e n t s were present and to p r o h i b i t the entrance o f unacceptable l e v e l s o f n u t r i e n t s o f contaminants such as p e s t i c i d e s and heavy metals. In a d d i t i o n t o q u a l i t y c o n t r o l o f t h e d i e t , chemical s u r v e i l l a n c e has always been employed to assure accurate dosages of the t e s t compounds i n animal d i e t s . The p r i n c i p l e requirements to prepare a dosed animal d i e t i n c l u d e a s e r i e s o f s t e r i l i z i n g , s c r e e n i n g , b l e n d i n g and p a c k a g i n g o p e r a t i o n s w i t h i n e n c l o s e d safety cabinetry. Autoclaving o f dosed animal feed i s normally necessary to ensure m i c r o b i o l o g i c a l i n t e g r i t y and the e f f e c t o f such a u t o c l a v i n g on both trace n u t r i e n t s and contaminants must o f n e c e s s i t y a l s o be c l o s e l y monitored (Table I I I ) . The data e x h i b i t the expected decrease i n the c o n c e n t r a t i o n l e v e l s o f v i t a m i n A and vitamin B. The sharp r e d u c t i o n i n malathion a f t e r a u t o c l a v i n g r e f l e c t s t h i s p a r t i c u l a r p e s t i c i d e ' s known thermal i n s t a b i l i t y .

TABLE m.

Effects of Autoclaving on Selected Feed Components Concentration (mean ± SD)

Analyte

Units

DDT (total) Dieldrin Lindane Matathion As Cd Ca Cu Se Zn Fat Protein Vitamin A Vitamin Bi

ppb ppb PPb ppm ppm ppb

%

ppm ppm ppm

% %

lU/g ppm

No. of samples 24 23 24 24 24 24 22 22 24 22 20 22 24 24

Before Autoclaving 7.1 1.2 2.3 0.8 0.3 73 1.3 13.1 0.4 110 5.3 24.3 44.2 89

+ + + +

+ + + +

+ + +

+ + +

8.6 1.6 0.9 0.9 0.2 43 0.2 2.5 0.1 9 O.b 1.0 14.7 10

After Autoclaving 9.9 2.0 1.7 0.1 0.6 108 1.3 14.2 0.4 121 4.8 24.4 23.2 65

+ 16.B + 3 + 1.0 + 0.1 + 0.1 + 54 + 0.2 + 1.9 + 0.1 + 9 + 0.7 + 0.8 + 15.3 + 16

During normal operations o f conducting n o n c l i n i c a l s t u d i e s u s i n g mice, rats, monkeys, e t c . a tremendous amount o f contaminated experimental m a t e r i a l s i s accumulated. In decontaminating animal cages l a r g e volumes o f water are used and the r e s u l t a n t waste water c o n t a i n s t r a c e l e v e l s o f a l l t e s t


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compounds. T h i s burning issue was addressed a t NCTR by d e v i s i n g an adsorptive system to remove t r a c e q u a n t i t i e s o f chemical carcinogens and other t e s t compounds ( i ) . The success o f the p i l o t study has culminated i n the c o n s t r u c t i o n and o p e r a t i o n o f a waste water treatment p l a n t a t NCTR a t a c o s t o f 1.5 m i l l i o n d o l l a r s to handle 100,000 g a l l o n s o f waste water per day. A schematic layout o f the p l a n t ( F i g u r e 1) i l l u s t r a t e s the tandem arrangement o f f i l t e r s , a c t i v a t e d carbon and non-ionic polymeric r e s i n (XAD-2) t o a c h i e v e a h i g h l y e f f i c i e n t and l o w - c o s t operation. For the moment, treated samples are analyzed f o r a l l carcinogens known to be present from experimental o p e r a t i o n s . This method o f monitoring i s a c o s t l y procedure and attempts are c u r r e n t l y under way to develop a s e r i e s o f model marker compounds (non-polar, semi-polar, and polar) to d e l i b e r a t e l y add to the i n f l u x of the waste water from the f a c i l i t y and monitor only these three to ensure the e f f i c i e n c y o f the e n t i r e system.

Biochemical Mechanisms o f Carcinogenesis The l a y p u b l i c and many f e l l o w s c i e n t i s t s have long been b i t t e r c r i t i c s o f the c u r r e n t l y accepted dose l e v e l s t u d i e s o f i n - v i v o carcinogen t e s t i n g . E x t r a p o l a t i o n o f t e s t r e s u l t s o f high dose to low dose l e v e l s and to the g e n e t i c a l l y d i v e r s e human population i s an accepted r e g u l a t o r y posture (5.) · At t h i s juncture, i t should be emphasized that the major advantage o f animal t o x i c i t y versus human epidemiology i s that the t o x i c i t y can be predicted before human exposure (e.g. a s b e s t o s ) . Attempts to explore the shape o f the dose response curve a t one order o f magnitude lower than that p r e v i o u s l y performed were conducted at NCTR, the s o - c a l l e d E D study to determine the dosage necessary to produce a 1% tumor r a t e (J_). The p r i c e tag o f such extensive e x p l o r a t i o n s precludes t h e i r repeat with other chemicals and has d i r e c t l y l e d to the dilemma o f concurrent investment i n b a s i c mechanism s t u d i e s t o seek o u t b i o c h e m i c a l indicators of c a r c i n o g e n i c i t y a t extremely low doses r a t h e r than conventional pathological indicators. Q 1

Carcinogenesis can be p r o p e r l y defined as a change i n the r e g u l a t o r y mechanism o f a t a r g e t c e l l which g i v e s r i s e to a progeny o f a l t e r e d c e l l s c o n s t i t u t i n g the b a s i s o f the n e o p l a s t i c disease. Therefore the i n i t i a l molecular i n s u l t i n f l i c t e d by a s p e c i f i c carcinogen may be l i m i t e d to only a few c e l l s . Such molecular events are the f o c a l point f o r many i n q u i r i e s i n t o the biochemical aspects o f c a r c i n o g e n e s i s . In very simple terms certain compounds have t h e s t r u c t u r a l ability t o become e l e c t r o p h i l i c or e l e c t r o n d e f i c i e n t moieties v i a metabolic activation, and then bind c o v a l e n t l y to i n f o r m a t i o n a l macromolecules (DNA, RNA, p r o t e i n s ) . These molecular events, f o r example, r e s u l t i n r e s i d u e s or adducts to the base p a i r s o f


4^

Schematic of industrial waste water treatment facility at the National Center for Toxicological Research Figure L


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DNA and s o p h i s t i c a t e d a n a l y t i c a l techniques are o f t e n required to i d e n t i t y them (6.). With the r e c e n t a v a i l a b i l i t y o f h i g h r e s o l u t i o n NMR the exact s i t e of i n t e r a c t i o n can be determined (Figure 2). Extensive s t u d i e s at NCTR devoted to t h i s s c i e n t i f i c probe have r e s u l t e d i n a data base or compilation of the v a r i o u s s i t e s of i n t e r a c t i o n on the bases of DNA (Figure 3 ) . It i s o p t i m i s t i c to p r e d i c t that t h i s l i n e o f i n q u i r y and the wealth of information on s i t e attachment w i l l r e p l a c e the more coventional bioassay as a r e g u l a t o r y t o o l . However, i t i s r e a l i s t i c to assume that t h i s l i n e o f attack on the biochemical mechanisms o f c a r c i n o g e n e s i s that has been i n i t i a t e d w i l l y i e l d up in s e v e r a l years some c l u e s or guides to unravel the s e c r e t s o f the b a s i c mechanisms of c a r c i n o g e n e s i s .

Future Trends i n Chemistry

and

Toxicology

H e a l t h - o r i e n t e d government a g e n c i e s r e s p o n s i b l e f o r the p r o t e c t i o n of the p u b l i c from p o s s i b l e adverse e f f e c t s , such as chemical residues i n the food supply, must somehow attempt to e s t a b l i s h p r i o r i t i e s on r e g u l a t i o n as w e l l as manpower to conduct monitoring programs. In 1975 i n the United S t a t e s alone, the p e s t i c i d e i n d u s t r y used approximately 1400 active ingredients f o r m u l a t e d by 4600 companies a t 7200 p l a n t s to p r o d u c e an estimated 35,000 - 50,000 separate products f o r an annual volume of 1.6 million pounds ( a p p r o x i m a t e l y 45% of t o t a l world production) with a r e t a i l value o f about three b i l l i o n d o l l a r s . Staggering as these s t a t i s t i c s o f 1975 might sound r e g u l a t o r y agencies are faced with i n c r e a s i n g problems o f how best to serve and p r o t e c t the p u b l i c h e a l t h . In an attempt to a s s i s t i n t h i s monumental task o f p r o v i d i n g maximum p r o t e c t i o n to the consumer while using the l i m i t e d resources that are a v a i l a b l e , a r i s k assessment procedure has been constructed (D as a p o s s i b l e technique to e v a l u a t e t o x i c m a t e r i a l s that are potential candidates as residues i n the food chain and to a s s i g n an index number t h a t i d e n t i f i e s a r e l a t i v e h a z a r d . This procedure, developed to accomplish a p o s s i b l e ranking o f the p o t e n t i a l r i s k s amongst the v a r i o u s chemical r e s i d u e s , i s c a l l e d the S u r v e i l l a n c e Index (SI). The SI, which c o n s i s t s o f three terms, can be expressed mathematically as follows :

S u r v e i l l a n c e index ( s i ) = TF + EF + BSF where TF = T o x i c i t y f a c t o r EF = Environmental f a c t o r BSF = B i o S a f e t y f a c t o r


270-MHz proton NMR spectrum of N-(deoxyguanosin-8-yl)-2-amino fluorene Figure 2


344

THE

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_ H Ι^^Ι^^Η* Γ

DNA C h a i n *

0

Ν

\ ^ π

Ν

-

N

^

TOXICOLOGY

Alkylating Agent (ENU, M N U , DMN); AFBj

yy_>.2-AAF; *1

A N D M O D E R N

^/Alkylating Agents; N-HO-I-NA ^° Ν

Ο ^

CHEMIST

M

A

B

;

2-AF

^ D N A Chain Benzopyrene; 2-AAF

Cytosine - Guanine

^Alkylating

CH3 J,

κι DNA Chain

Η

Agents -Aromatic Amines

° Alkylating Agents DNA Chain Alkylating Agents Thymine - Adenine

Figure 3.

Summary of the experimental investigations into the various sites of adduct formation on DNA by various known carcinogens


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T o x i c i t y F a c t o r (TF) = KT χ RTR where KT = K i l o t o n s o f the compound released i n t o the environment annually RTR = R e l a t i v e t o x i c i t y r a t i o = LD dieldrin/LD f o r the compound ( o r a l i n r a t s ) Q

Environmental f a c t o r (EF) = CV χ *> where CV = the sum o f the crop values

Crop

1

/

2

1 3 7 10 10 5 20

- Effective h a l f - l i f e

E

λ/2Έι

Value

Cotton Grains Legumes Vegetables Fruits Tobacco Milk

t

5 Q

=

/

where fc

1/2p

t

1

/

2

b

=

P

n v s i c a l

half-life

= biological

half-life

B i o S a f e t v F a c t o r (BSF ) = PB χ S χ PAR/NOEL where PB S PAR NOEL

= P r o p e n s i t y to biomagnify = S p e c i f i c i t y ( r e a c t i v e s i t e s i n man) = Population a t r i s k = (Presumed) no observable e f f e c t l e v e l (ppm)

Applying t h i s procedure to f i v e s e l e c t e d environmental p o l l u t a n t s (Table IV) has provided numerical values as p o t e n t i a l i n d i c a t o r s o f high r i s k s . This equation i s by no means s e t i n stone and work i s continuing to r e f i n e and provide an exponential term to encourage graphic d i s p l a y s f o r management purposes.


T H E

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Surveillance Indices f o r Selected Pollutants

Compound p,p'-DDT Toxaphene Methyl parathion Carbaryl Aminotriazole

1978

1971

Banned 1,025 310 160 Banned

2,476 1,019 270 160 27

C u r r e n t l y , p e s t i c i d e residues are monitored by a wide v a r i e t y o f chemical e x t r a c t i o n and i d e n t i f i c a t i o n schemes. There i s no s i n g l e c h e m i c a l m u l t i - r e s i d u e p r o c e d u r e a v a i l a b l e n o r under development that can determine the e n t i r e spectrum o f p e s t i c i d e residues i n a given sample. At present, even the most s o p h i s t i cated procedures can only monitor a t t r a c e l e v e l s f o r s e v e r a l compounds i n a few c l a s s e s o f p e s t i c i d e s . The problem i s that assays performed by such procedures are labor i n t e n s i v e and sometimes employ expensive equipment and personnel. Therefore, what i s s a d l y needed i s a r a p i d , s e n s i t i v e and r e l a t i v e l y inexpensive m u l t i - r e s i d u e procedure to monitor f o r t o x i c a n t s i n the food chain. An i n v e s t i g a t i o n o f bioassay systems employing four species o f arthropods, Daphnia Hvalella C u l e x and Palaemonetes was i n i t i a t e d i n response to the need f o r such an assay system (8J. The e v a l u a t i o n o f inherent t o x i c i t i e s r e l a t e d to types and amount o f organic s o l v e n t s commonly used i n such systems i n d i c a t e d that dimethyl s u l f o x i d e (DMSO) and methanol (MeOH) were l e a s t t o x i c i n the aqueous t e s t media. These s o l v e n t s were then used i n 18 hr. t e s t s to determine s e n s i t i v i t i e s o f the four organisms to a r e p r e s e n t a t i v e compound from s i x c l a s s e s o f pesticides. S t r e s s f a c t o r s such as amount o f organic solvent and volume o f t e s t medium were adjusted to determine t h e i r e f f e c t s on three o f the organisms tested against d i e l d r i n and parathion. The highest s e n s i t i v i t y obtained with d i e l d r i n (50% m o r t a l i t y with 2 ng i n a 25 ml t e s t medium) was with Culex stressed with 2% o f MeOH i n a reduced t e s t volume. H v a l e l l a stressed with 2% o f MeOH were most s e n s i t i v e to parathion (50% m o r t a l i t y with 85 pg i n a 100 ml t e s t medium); f u r t h e r s t r e s s imposed by reducing the volume o f t e s t medium d i m i n i s h e d s e n s i t i v i t y . These v e r y p r e l i m i n a r y experiments with v a r i o u s e x t r a c t s o f animal feed i n d i c a t e d that an extensive e f f o r t would be required to develop a method that could provide e x t r a c t s compatible with the bioassay systems. f

r


21. CAIRNS Increased Role of Chemistry in Toxicology

347

Conclusions

With the c o n t i n u i n g increased knowledge and emphasis on modern t o x i c o l o g y the demands on the component d i s c i p l i n e s such as chemistry must i n e v i t a b l y i n c r e a s e not as p a s s i v e supporters but as aggressive p a r t n e r s demanding g r e a t e r p a r t i c i p a t o r y r o l e s i n the design and research management areas o f conceived experiments. Chemistry must assume i t s proper r o l e i n the h i e r a r c h y o f modern t o x i c o l o g y and through a p p l i c a t i o n o f i t s fundamental d i s c i p l i n e c o n t r i b u t e t o major breakthroughs as w e l l as continue to provide i n t e g r i t y o f animal experiments. Disclaimer

The views expressed are those o f the author and do not n e c e s s a r i l y r e f l e c t t h e p o l i c y o f t h e U.S. Food and Drug Administration.

Literature Cited 1.

Cairns, T.; 3(3), 1.

2.

Greenman, D.L.; Oller, W.L.; L i t t l e f i e l d , N.A.; and Nelson, C.J.; J . Environmental Pathology & Toxicology. 1980 6, 235.

3.

Oiler, W.L.; Gough, B . ; and Littlefield, N.A.; Environmental Pathology & Toxicology. 1980, 3(3), 203.

4.

Nony, C.R.; Treglown, E . J . ; and Bowman, M.C.; Science of the Total Environment, 1975, 4, 155.

5.

IRLG Report, J . Nat. Cancer Inst., 1979, 63, 245.

6.

Kadlubar, F.F.; J. Nat. Cancer Inst., 1980, in press.

7.

Oller, W.L., Cairns, T., Bowman, M.C.; and Fishbein, L . ; Archives of Environm. Contamin, and Toxicology, 1980, 9, 483.

8.

Bowman, M.C., Oller, W.L., Cairns, T., Gosnell, A.B., and Oliver, K.H.; Archives of Environm. Contamin. and Toxicology. 1981, January.

RECEIVED

J . Environmental Pathology & Toxicology.

February 2, 1981.


1980,

The Pesticide Chemist and Modern Toxicology - ACS Publications

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