Organometals and Organometalloids - ACS Publications - American

3 Occurrence of Biological Methylation of Elements in the Environment

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on July 15, 2016 | http://pubs.acs.org Publication Date: January 12, 1979 | doi: 10.1021/bk-1978-0082.ch003

Y. K. CHAU and P. T. S. WONG

Canada Centre for Inland Waters, Burlington, Ontario, Canada

Biological methylation of elements is one of the most intrigu ing biochemical processes involved with l i v i n g systems. This phenomenon was observed in the early nineteenth century (1815) when several cases of arsenical poisoning occurred in Germany due to the use of domestic wallpapers containing arsenic pigments. In 1839 Gmelin (1) noted that a garlic odor was present in rooms associated with the incident. The mystery was not thoroughly unveiled until 1893 when Gosio (2) observed the evolution of a garlic odor gas from a mould-infected sample of mashed potato on exposure to a i r . The gas was called Gosio gas which was later identified by Challenger as trimethylarsine. The term "biological methylation" was f i r s t used by Challenger (3) to describe the replacement of the οxy-groups of arsenic, selenium and tellurium compounds by methyl groups through the action of moulds, resulting in the formation of organometalloids or organometallic compounds. It has since been shown that bio logical methylation is a general process for l i v i n g organisms (4). Available information indicates that microorganisms, especially bacteria and fungi play an important role in the transformation. While the biological function of methylation is not clearly known, it has been proposed to be a detoxification process. Alternately, it may be energetically preferable for some organisms to trans methyl ate metal rather than to synthesize methane (5). Studies on the environmental impacts of biological methyla tion have gained much momentum since the discovery that micro organisms in a natural lake sediment were able to methylate mercury to a highly-neurotoxic methylmercury species (6). Because methylmercury is produced at a rate faster than organisms can accomplish its degradation, i t may accumulate in fish and so poses a threat to public health (7). Indeed, several incidents of environmental catastrophies caused by mercury have been documented f8.9). Methylation in the environment results in the formation of organometalloids or organometals which are generally more toxic and easily bioaccumulated; it plays an important role in the mobilization of elements from sediment to water; i t may cause 0-8412-0461-6/78/47-082-039$05.00/0 © 1978 American Chemical Society

Brinckman and Bellama; Organometals and Organometalloids ACS Symposium Series; American Chemical Society: Washington, DC, 1979.


40

organometals and organometalloids

transmethylation of other elements. Attempts have been made to predict the p o s s i b i l i t y of methylation of other elements by the relative ease of formation of metal-carbon bonds (7) and by the reduction potential of the elements (10). The metals Hg, Sn, Pd, Pt, Au and T l and metalloids As, Se, Te and S have been postulated to accept methyl groups from methyl-cob alamin in biological systems. However, Pb, Cd and Zn have been predicted not to be methylated because of the extreme i n s t a b i l i t y of their monoalkyl derivatives in aqueous systems. Methylation studies pertaining to environmental impact began when Jensen and Jernelov (6) investigated the transformation of HgCl in bottom sediments from freshwater aquaria. Then Cox and Alexander (11) studied the transformation of methylated arsenic and selenium compounds from their inorganic salts by fungi isolated from raw sewage and grown on agar plates. Similarly, Huey et a l . (12,13) investigated methylation of Sn, Cd, by a Pseudomonas species isolated from Chesapeake Bay. A l l these investigations were carried out with environmentally originated microorganisms grown in laboratory media. More r e a l i s t i c approaches were adopted by Bramen (14), Langley (15), and Wong et a l . (16) who used systems containing natural waters and sediments to investigate respectively the methylation of As, Hg, and Pb. A l l these investigations, however, bear certain relevance and significance to the environment and can be extrapolated to living ecosystems. Methylation of mercury in the environment has been well established and documented by other workers. 2

Experimental A sediment-lake water system is used for the investigation of methylation of metals and metalloids in the aquatic environment. In each study, 50 g of sediment and 150 ml of lake water were placed in a 250 ml f i l t e r flask. Nutrient broth (0.5%), glucose (0.1%), and yeast extract (0.1%) were added to stimulate microbial growth. The compounds to be tested for methylation were added to the sediment (5 mg/Jt) and the flasks were capped and incubated at 20°C for 7-10 days. The headspace gas was analyzed for volatile methylated compounds and the lake water was analyzed for the presence of methylated species of the element. A specially-developed Gas Chromâtograph-Atomic Absorption technique was used for the analyses of volatile alkyllead compounds (17), methyl selenides (18), methylarsines and methylarsenic acids (19). Sediments from several lakes in Ontario were used for the studies. In a l l these experiments, appropriate controls were prepared either by omitting the test compounds or by s t e r i l i z i n g the medium by autoclaving. The toxicity of the v o l a t i l e alkyl metals (Pb) and metalloids (As, Se) on algal growth was investigated by using the biologically generated alkyls since most of the methylated products are highly



3.

CHAU AND WONG

Biological Methylation

41

v o l a t i l e and i n s o l u b l e i n water, making the dosing o f the compounds t o b i o t a d i f f i c u l t . The b i o l o g i c a l generator (Figure 1) c o n s i s t s o f a 4 £ c u l t u r e f l a s k c o n t a i n i n g a b a c t e r i a l inoculum (Aeromonas sp. 150 ml) and 1350 ml o f the f r e s h n u t r i e n t medium w i t h and without the d e s i r e d compound (at 5 ppm l e v e l as the element) f o r generation o f the v o l a t i l e methylated products. When sediment was used, 500 g sediment and one l i t r e of l a k e water w i t h and without the compound were incubated w i t h glucose (0.1%). A f t e r about 10 days i n c u b a t i o n , the headspace gases were analyzed f o r the presence of the methyl d e r i v a t i v e s before the c u l t u r e f l a s k was connected t o a t e s t f l a s k (4 l i t r e ) c o n t a i n i n g 1.4 £ o f f r e s h CHU-10 medium and 100 ml of a l g a l inoculum. The b i o l o g i c a l l y - g e n e r a t e d methylated product was sucked through the a l g a l c u l t u r e f l a s k by a p e r i s t a l t i c pump. The setup without the a d d i t i o n o f the compound was used as a c o n t r o l . The e f f e c t s of a p a r t i c u l a r methylated product on a l g a l growth and primary p r o d u c t i v i t y were determined. Results and

Discussion

Methylation of lead. Wong et a l . (16) presented the f i r s t evidence that under l a b o r a t o r y c o n d i t i o n s microorganisms i n s e d i ments from s e v e r a l Canadian lakes would transform c e r t a i n i n o r g a n i c and organic lead compounds i n t o a v o l a t i l e and h i g h l y t o x i c tetramethyllead. I t was a l s o observed t h a t i n c u b a t i o n o f c e r t a i n lake sediments produced Me^Pb even without the a d d i t i o n o f extraneous lead compound. There was no d i r e c t r e l a t i o n s h i p between lead concentrations i n the sediment and the amount o f Me^Pb produced (Table I ) . The conversion o f MeaPbOAc to Me^Pb was observed i n a l l experiments but that o f lead n i t r a t e was only sporadic. Subsequently, J a r v i e et a l . (20) confirmed the methylation o f MeaPbOAc t o Mei*Pb and proposed a mechanism i n v o l v i n g hydrogen s u l f i d e complexed w i t h MeaPbOAc f o l l o w e d by decomposition t o Mei*Pb. These workers suggested t h a t lead methylation was a chemical process, without c o n s i d e r i n g the m i c r o b i a l production o f s u l f i d e i n sediment as being a b i o l o g i c a l process. Later Schmidt and Huber (21) demonstrated t h a t not only t r i m e t h y l l e a d , but a l s o lead a c e t a t e , could be methylated t o t e t r a m e t h y l l e a d i n aquarium water. The mechanism o f methylation i s yet to be established. Chemical d i s p r o p o r t i o n a t i o n r e a c t i o n s o f Me3Pb s a l t s are known to produce Me^Pb. The experiments s e t up t o determine the p o r t i o n o f Mei+Pb due t o chemical d i s p r o p o r t i o n a t i o n r e a c t i o n s c o n s i s t e d of a s e r i e s of c u l t u r e of Aeromonas species i n n u t r i e n t b r o t h w i t h a d d i t i o n o f 0-100 mg Pb/£ o f Me PbOAc. An i d e n t i c a l set o f samples was s t e r i l i z e d f o r determining the MeiiPb produced by chemical d i s p r o p o r t i o n a t i o n r e a c t i o n s . A f t e r three weeks i n c u b a t i o n , the b a c t e r i a growth was measured and the amounts o f Me^Pb produced i n the headspace of the chemical and b i o l o g i c a l systems were q u a n t i f i e d . The amounts o f Me^Pb generated +

3



4.7 4.0 21.0 7.6 2.4 1.4 6.4

0.09 1.10 0.14 2.10 0.55 0 0 0.13

0 1.80 0.16 0 0.71 0 0 0.01

116 285 47 48 47 48 43

Long Lake

K e l l y Lake

Lunch Lake

Robinson Lake

D i l l Lake

Norway Lake

Babine Lake

Hamilton Harbor

4.

5.

6.

7.

8.

9.

10.

11.

50 gm sediment ( w e t w t . ) , 150 ml l a k e water, 0.5% n u t r i e n t broth and 0.1% glucose with and without the a d d i t i o n o f 1 mg Pb as Pb (NO3)2 o r Me PbOAc. F i n a l Pb c o n c e n t r a t i o n 5 ppm.

3

8.6

0

0

69

P o r t Stanley

3.

273

2.9 5.2

0

0

60

E r i e a u Harbor

2.

4.7

2.20

1.20

110

3

Me PbOAc

M i t c h e l Bay

2

Pb(N0 )

No a d d i t i o n 3

yg Me^Pb generated from sediment supplemented w i t h

(mg/kg dry wt.)

T o t a l Pb cone. i n sediment

M e t h y l a t i o n o f l e a d i n l a k e sediments.

1.

Lake

Table I .


3.

CHAU AND WONG

43


b i o l o g i c a l l y and c h e m i c a l l y a t d i f f e r e n t concentrations o f MeaPbOAc and t h e i r r e l a t i o n s h i p s t o b a c t e r i a l growth a r e i l l u s t r a t e d i n Figure 2. At any c o n c e n t r a t i o n o f MeaPbOAc where t h e microorganisms were a c t i v e l y growing, the Me^Pb generated chemic a l l y only represented about 15-20% o f t h e t o t a l MeifPb produced i n the b i o l o g i c a l system. When growth was i n h i b i t e d a t 100 ppm o f MeaPbOAc, the Me^Pb generated i n the system was s o l e l y due t o chemical d i s p r o p o r t i o n a t i o n . U l t r a v i o l e t i r r a d i a t i o n d i d n o t cause f u r t h e r chemical conversion o f Me PbOAc t o Me^Pb i n t h e absence o f microorganisms. D i r e c t chemical s y n t h e s i s o f methyllead compounds through a l k y l a t i o n o f i n o r g a n i c lead i s very d i f f i c u l t because o f t h e extreme i n s t a b i l i t y o f t h e p o s t u l a t e d f i r s t i n t e r m e d i a t e monoa l k y l l e a d s a l t ( M e P b ) . The d i f f i c u l t i e s have a l s o been e x p l a i n e d i n terms o f o x i d a t i o n - r e d u c t i o n r e a c t i o n s i n v o l v e d i n b i o m e t h y l a t i o n (10). However, from a biochemical p o i n t o f view, i t i s not e n t i r e l y unreasonable t o envisage l i g a n d systems which could form s t a b l e monomethyllead complexes before t h e s u c c e s s i v e methylation steps occur. Such may have been the case i n t h e observations o f methylation o f lead n i t r a t e and lead c h l o r i d e t o Me^Pb i n some sediments. The t o x i c i t y o f Mei*Pb on an a l g a (Scenedesmus quadricauda) was s t u d i e d by b u b b l i n g t h e b i o l o g i c a l l y - g e n e r a t e d Mei»Pb i n t o t h e c u l t u r e medium (22). I t was estimated t h a t l e s s than 0.5 mg (as Me^Pb) had passed through t h e c u l t u r e medium. The primary product i v i t y ( C technique) and c e l l growth (dry weight) decreased by 85% and 32%, r e s p e c t i v e l y , as compared w i t h t h e c o n t r o l s without exposure t o Mei*Pb. Furthermore, c e l l s exposed t o Me»»Pb tended t o clump together. S i m i l a r r e s u l t s were obtained w i t h Ankistrodesmus f a l c a t u s . To o b t a i n s i m i l a r e f f e c t s , t w i c e as much lead i n t h e form o f MesPbOAc, and twenty times as much lead n i t r a t e would be required. Lead methylation i s analogous t o mercury i n s e v e r a l aspects. I t i s dependent on temperature, pH and m i c r o b i a l a c t i v i t i e s o f t h e medium but independent o f t h e c o n c e n t r a t i o n o f l e a d i n t h e sediment. So f a r t h e r e are o n l y three r e p o r t s o f l a b o r a t o r y experiments on lead methylation. Evidence o f i t s occurrence i n t h e environment i s s t i l l l a c k i n g . However, e x i s t e n c e o f s i g n i f i c a n t l y h i g h r a t i o s o f t e t r a a l k y l l e a d t o t o t a l lead i n c e r t a i n f i s h e r y products i n d i c a t e s the p o s s i b i l i t y o f methylation i n sediment o r i n f i s h t i s s u e s (23). The f a c t o r s and t h e occurrence o f i n s i t u l e a d methylation i n t h e environment and t h e mechanisms o f methylation a r e being f u r t h e r investigated.


3

+3

llf

M e t h y l a t i o n o f Selenium. The production o f v o l a t i l e selenium compounds by microorganisms has been acknowledged f o r decades (24). I t i s known t h a t v o l a t i l e selenium compounds (Me Se and Me Se ) a r e produced through methylation by f u n g i , b a c t e r i a , r a t s , and h i g h e r p l a n t s (25). Not much i s known about t h e methylation o f selenium i n the a q u a t i c environment. Under l a b o r a t o r y c o n d i t i o n s , Chau e t 2


2

2


ORGANOMETALS AND ORGANOMETALLOIDS

VOLATILE ALKYL-METAL GENERATOR Figure 1.

O

BIOASSAY FLASK

PUMP

Biological generation of volatile methyl alkyls for algal toxicity testing

20

40

Meg Pb OAc (mg

60

80

100

Pb-Γ)

Figure 2. Production of Me Ph by chemical disproportionation and by biological methylation and their rehtionships to growth of Aeromonas species. Growth was measured by optical density. h


3. CHAU AND WONG

45


a l . (26) observed the production of Me Se and Me Se from s e v e r a l sediment and soil samples w i t h and without enrichment w i t h the f o l l o w i n g selenium compounds: sodium s e l e n i t e , sodium s e l e n a t e , s e l e n o c y s t i n e , selenourea, and selenomethionine. In many cases, an u n i d e n t i f i e d v o l a t i l e selenium compound was produced w i t h a r e t e n t i o n time between t h a t o f Me Se and Me Se i n the gas chromatogram. The production o f v o l a t i l e selenium compounds was observed to be a s s o c i a t e d w i t h m i c r o b i o l o g i c a l growth and was temperature dependent. A summary o f the i n v e s t i g a t i o n s w i t h l a k e sediments w i t h and without a d d i t i o n of sodium s e l e n i t e and s e l e n ate i s given i n Table I I . I t has been shown t h a t s i g n i f i c a n t concentrations of selenium e x i s t i n both f r e s h and s a l t water f i s h (27). In studying the r e l a t i v e t o x i c i t y o f organic and i n o r g a n i c selenium compounds t o f i s h , N i i m i and LaHam (28) observed a n o t i c e a b l e d a i l y decrease o f selenium l e v e l s i n the t e s t s o l u t i o n . The l o s s was probably due t o the m i c r o b i a l methylation o f the i n o r g a n i c selenium t o a v o l a t i l e organoselenium compound which was more t o x i c t o f i s h . Selenium i s of p a r t i c u l a r i n t e r e s t as a p o t e n t i a l environmental t o x i c a n t because o f the small s a f e t y margin between the l e v e l s necessary i n the d i e t and the concentrations hazardous t o man (29). Organic selenium compounds are more t o x i c and have longer r e t e n t i o n times than the i n o r g a n i c selenium s a l t s (30). Thus i t i s of considerable i n t e r e s t t o study the methylation o f selenium i n the aquatic environment. 2


2

2

2

2

2

Methylation of arsenic. M e t h y l a t i o n o f a r s e n i c by f u n g i and b a c t e r i a has been known f o r s e v e r a l decades. Challenger and co-workers (3) e x t e n s i v e l y i n v e s t i g a t e d the a b i l i t y o f S c o p u l a r i opsis b r e v i c a u l i s t o methylate organic and i n o r g a n i c a r s e n i c compounds. Cox and Alexander (11) found 3 sewage f u n g i t h a t would methylate v a r i o u s a r e s e n i c compounds used as p e s t i c i d e s t o form t r i m e t h y l a r s i n e . McBride et_ a l . (31) a l s o showed that aerobic microorganisms produced t r i m e t h y l a r s i n e whereas the anaerobic methanogenic b a c t e r i a produced d i m e t h y l a r s i n e when incubated i n the presence of pentavalent and t r i v a l e n t a r s e n i c d e r i v a t i v e s . In our experiments w i t h lake water and sediment, we have demonstrated t h a t i n c e r t a i n sediments c o n t a i n i n g high a r s e n i c l e v e l s , such as those from the Moira R i v e r area i n O n t a r i o , nonv o l a t i l e methylated a r s e n i c compounds are detected i n the overl a y i n g lake water without the a d d i t i o n of extraneous a r s e n i c compounds (Table I I I ) . In other sediments w i t h low a r s e n i c l e v e l s , a d d i t i o n o f a r s e n i c compounds was r e q u i r e d f o r methylation. However i n most o f these experiments, no v o l a t i l e methylated a r s i n e s were detected i n the headspace of the i n c u b a t i o n f l a s k s . I n s e v e r a l experiments w i t h the sediments from the Moira R i v e r , v o l a t i l e methylated a r s i n e s (Me AsH,, Me3As) were detected. Factors which c o n t r o l a r s e n i c methylation are not completely understood. Adenosine t r i p h o s p h a t e and hydrogen were found t o be e s s e n t i a l f o r the formation of d i m e t h y l a r s i n e by c e l l e x t r a c t s o f 2



i

0.90

3.Kelley

4.Long

2

0

0

0

0

6.3

0

0.65

0.67

0.44

0.53

0.55

0.67

7. Windy

8. Moose

9. Kukagami

lO.Nepewassi

11.Johnnie

12.George

0

0.52

0

1.7

2.7

0

34

6.Vermillion

16.28

1.64

20.48

2.Ramsey

0.48

5.Simons

3

No A d d i t i o n 3

0

0

0

0

0

0

0

0

0

3.3

0

0

2

0

3.7

0

0

0

0

0

0

0

2.3

0

3.3

yg/g dry ( C H ) S e (CH )ζSe Unknown wt.

1.Elbow

Lake

Se i n Sediment 2

56.8

43.3

25.3

33.3

5

12.3

20.3

18.7

27.3

14

0

33.3

3

(CH ) Se 3

0

16.5

0

0

0

0

0

0

0

0

0

0

2

(CH ) Se 2

Na s e l e n i t e 3

2

8.7

0

0

0

0

0

18

0

0

0

0

94.7

94.6

28.7

23.4

10.5

0

9.7

20

24.7

20

33.6

34

11

19.4

0

0

0

0

8

4.7

0

3.3

0

0

3

2

Unknown ( C H ) S e ( C H ) S e

Na selenate

Table I I . M e t h y l a t i o n o f selenium compounds i n 12 Sudbury area l a k e sediment samples.


2

7.3

54.8

0

0

2

0

5.3

19.7

0

5.3

0

3.3

Unknown

£2-

2.

ρ

Sample

ET —*

Ο

20.40 3.73

3.96

arsenite

17.92 7.19

arsenate

8.89

6.03

none

7.59

trimethy1 a r s i n e oxide

2.93 0.63

0.52

3.27

0.50

0.45

arsenate

arsenite

2.29

7.84

9.57

3.25

dime t h y l a r s i n i c acid

3.75

0.80

1.03

2.14

methylarsonic acid

1.16

0.80

1.92

As(III) As(V)

A r s e n i c i n medium (ug/l)

none

arsenite

arsenate

none

Arsenic a d d i t i o n (5 mg/1)

* - below 0.1 ng d e t e c t i o n l i m i t

Pond sediment

ça q *2 ~ R i v e r sediment

3* CD

GO R~

Ζ

§

CD

a.3

"•"*· cr%


Table I I I . Methylations o f a r s e n i c compounds i n sediment samples from Moira R i v e r area, O n t a r i o .

I- U 2?La -, Lake sediment Ξτ « c i 5? 3 I « g 3



limit

dimethylarsinic acid

-

9.10

arsenite

methylarsonic a c i d

4.89

arsenate


-

0.14 3.76

12.60

-

1.18

-

1.0

0.40

-

0.5

1.1

-

0.4

-

0.6

0.2

0.5

0.8

Arsine

-

-

-

trimethyl arsine oxide

10.9

-

—

113.0

-

Trimethyl-

V o l a t i l e As i n headspace (ng)

6.15

0.47

-

11.73

1.79

1.67

0.09

8.09

arsenite

methylarsonic a c i d

0\51

0.08

7.61

arsenate

below 0.1 ng d e t e c t i o n

Flavobacterium sp

E. C o l i

2.72

-

2.88

-

9.63


*

0.78

-


_

8.92

arsenite

-

methylarsonic acid

(mg/£)

me t h y l a r s o n i c a c i d

8.59

arsenate

Aeromonas sp

As(III) As (V)

As i n medium

o f a r s e n i c compounds by pure b a c t e r i a .

Arsenic addition (10 mg/£)

Methylation

Bacterial species

Table IV.


ο

> ο

Ο Ο » Ο

>

r

g >

> ο

w ο

Ο


3.

CHAU AND WONG

49


Methane-bacterium (32). Phosphate, s e l e n a t e and t e l l u r a t e , however, i n h i b i t e d the conversion o f arsenate t o t r i m e t h y l a r s i n e by a fungus (11). Since sediment i s a complex b i o l o g i c a l and chemical mosaic, i t i s d i f f i c u l t t o understand what organisms(s) and r e a c t i o n s are r e s p o n s i b l e f o r the a r s e n i c m e t h y l a t i o n . In an attempt t o s i m p l i f y the s i t u a t i o n , we have found two pure b a c t e r i a l c u l t u r e s Aeromonas and Flavobacterium sp., i s o l a t e d from lake water and another bacterium E s c h e r i c h i a c o l i , commonly found i n the i n t e s t i n e o f an organism and i n p o l l u t e d water, had the a b i l i t y t o methylate a r s e n i c compounds when grown i n a medium o f 0.5% n u t r i e n t b r o t h , 0.1% glucose and 10 mg/£ a r s e n i c compound (as As) at 20°C under aerobic c o n d i t i o n s (Table I V ) . Results show t h a t the a d d i t i o n s o f a r s e n i c compounds t o the medium would g e n e r a l l y r e s u l t i n the formation o f d i m e t h y l a r s e n i c a c i d i n the medium. T r i m e t h y l a r s i n e oxide was seldom detected. In these experiments, v o l a t i l e a r s i n e and t r i m e t h y l a r s i n e were a l s o found i n the headspace o f the culture flasks. The t o x i c i t y o f a mixture o f b i o l o g i c a l l y - g e n e r a t e d v o l a t i l e a r s i n e s on an a l g a ( C h l o r e l l a pyrenoidosa) was i n v e s t i g a t e d by the p r e v i o u s l y mentioned technique. The primary p r o d u c t i v i t y ( C technique) and c e l l growth ( c e l l count) decreased by 45% and 44%, r e s p e c t i v e l y , as compared w i t h the c o n t r o l algae without exposure to a r s i n e s . Chemical analyses o f the a l g a l c e l l s r e v e a l e d t h a t the t o t a l As l e v e l s i n the exposed c e l l s were 10 times more than t h a t i n the unexposed c e l l s . McBride et a l . (31), u s i n g c e l l - f r e e e x t r a c t s o f the a e r o b i c s o i l organism, Candida humicola, demonstrated t h a t i n the presence o f S-adenosylmethionine and NADPH, the e x t r a c t s could s y n t h e s i z e a r s e n i t e , methylarsonate and d i m e t h y l a r s i n a t e from arsenate. Whether such r e a c t i o n s occur i n sediments r e q u i r e s f u r t h e r investigation. llf


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Literature Cited 1.

Gmelin.

Karlsruhen

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Gosio, B.

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Challenger, F.

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Wood, J . M .

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Irukayama, K. "The pollution o f Minamata Bay and Minamata Bay d i s e a s e " , p . 153 in Advances in Water Pollutions Research. Proc. 3rd I n t . Conf. Water Pollution C o n t r o l Fed. Washington, D.C. vol. 3. (1967).

9.

N i i g a t a Report. Report on the cases o f mercury p o i s o n i n g in N i i g a t a . M i n i s t r y o f H e a l t h and Welfare, Tokyo, Japan (1967).

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ital.

(1839) November.

biol.

(1893) 18, 253.

Chem. Rev. (1945) 36, 315.

J.

J.F.

Zeit.

Chem. Educ. (1973) 50, 390. and G a v i s , Jernelöv,

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Science (1974)

L.J.

Water Res. (1972) 6, 1259. Nature (1969) 220, 173. 183, 1049.

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Ridley, W.P., Dizikes, 197, 329.

and Wood, J . M .

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Cox, D . P . and Alexander, M. (1973) 9, 84.

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Huey, C., Brinckman, F.E., Grim, S. and I v e r s o n , W.P. Proc. I n t . Conf. "Transport o f P e r s i s t e n t Chemicals in A q u a t i c Ecosystems". O.N. LeHam, Ed. ( N a t i o n a l Research Council o f Canada, Ottawa 1974) pp. 73-78.

13.

Huey, C., Brinckman, F.E., I v e r s o n , W.P. and Grim, S.O. Abst. I n t . Conf. Heavy Metals Environ. Toronto, Ont. (1975) Paper C214.

14.

Braman, R . S .

Bull.

E n v i r o n . Contam. T o x i c o l .

"Arsenical Pesticides",

pp. 108-123.

Amer. Chem. Soc.

E . A . Woolson, Ed.

Washington, D.C. (1975).

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Langley, D.G. J. Water

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Wong, P.T.S., Chau, Y . K . and Luxon, P . L . Nature (1975) 253, 263. Chau, Y.K., Wong, P . T . S . and Goulden, P . D . A n a l . Chim. Acta (1976) 85, 421.

17.

Pollut.

Science (1977)

C o n t r o l . Fed. (1973) 45, 44.



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18.

Chau, Y.K., Wong, P . T . S . and Goulden, P . D . (1975) 47, 2279.

A n a l . Chem.

19.

Wong, P.T.S., Chau, Y.K., Luxon, P . L . and Bengert, G.A. Proc. 11th Ann. Conf. "Trace Substances i n E n v i r o n . Health X I " M i s s o u r i . Ed. D.D. H e m p h i l l , pp. 100-106 (1977).

20.

J a r v i e , A . W . P . , M a r k a l l , R . N . and P o t t e r , H . R .

Nature

(1975) 225, 217. 21.

Schmidt, U . and Huber, F .

Nature (1976)

22. 23.

S i l v e r b e r g , B.A., Wong, P . T . S . and Chau, Y . K . A r c h . E n v i r o n . Contam. T o x i c o l . (1977) 5, 305. S i r o t a , G.R. and Uthe, J.F. A n a l . Chem. (1977) 49, 823.

24.

C h a l l e n g e r , F.

25.

C h a l l e n g e r , F. Adv. Enzymology and r e l a t e d areas o f molecular biol. (1951) 12, 429.

26.

Chau, Y.K., Wong, P.T.S., S i l v e r b e r g , B.A., Luxon, P . L . and Bengert, G.A. Science (1976) 192, 1130.

27.

Oelschlager, V.W. and Menke, K . H . Ernahrungswiss (1969)

Chem. and Ind. (1935)

259, 159.

54, 657.

9, 216. 28.

N i i m i , A.J. and LaHam, Q.N.

Can. J. Z o o l .

(1976) 54, 501.

29.

Copeland, R.

30. 31.

Schroeder, H.A., F r o s t , D.A. and B a l a s s a , J.J. J . Chronic Disease (1970) 23, 227. McBride, B.C., Reimer, M.M. and C u l l e n , W.R. 175th ACS N a t i o n a l Meeting, Anaheim, Calif. (1978) A b s t r a c t o f Papers, I n o r g a n i c , no. 116.

32.

McBride, B . C . and Wolfe, R . S .

Limnos (1970) 3, 7.

Biochem. (1971) 10, 4312.

Discussion J . M . WOOD ( U n i v e r s i t y of M i n n e s o t a ) : One of the t h i n g s I f i n d p u z z l i n g about the m e t h y l a t i o n of l e a d i s what s o r t of comp l e x has to be formed i n b i o l o g i c a l systems to s t a b l i z e a s i n g l e lead-carbon bond i n water? T h i s i s a tremendous problem from a thermodynamic p o i n t of v i e w . Y e t , i t appears that somehow t h i s happens because t e t r a m e t h y l l e a d i s produced. I wonder whether


52

ORGANOMETALS AND

ORGANOMETALLOIDS

anybody here has any idea on what s o r t of l i g a n d i s l i k e y t o coo r d i n a t e lead to s t a b l i z e a s i n g l e lead-carbon bond i n water. CHAU: We are working on a number of b i o l o g i c a l l i g a n d s , name l y , g l u t a t h i o n e p o l y c a r b o x y l i c a c i d s , and s u l f u r l i g a n d s , t r y i n g t o s t a b l i z e the monomethyllead complex. F. HUBER ( U n i v e r s i t y of Dortmund): Did you add v i t a m i n B t o your s o l u t i o n s when studying the production of t e t r a m e t h y l l e a d from l e a d ( I I ) compounds? Downloaded by UNIV OF CALIFORNIA SAN DIEGO on July 15, 2016 | http://pubs.acs.org Publication Date: January 12, 1979 | doi: 10.1021/bk-1978-0082.ch003

1 2

CHAU: Yes, we d i d add B^» use no B^2«

but i n our general experiments we

HUBER: So there i s no i n f l u e n c e on the t e t r a m e t h y l l e a d d u c t i o n when you add v i t a m i n B ^ ? CHAU: No,

pro-

there was no enhancement.

HUBER: This i s about the same r e s u l t we got, e s p e c i a l l y when we t r i e d i t w i t h t h a l l i u m . You t a l k e d about the problem of the p r o p o r t i o n where you found about 15%-20%; we f i n d about 80% chemi c a l l y produced t e t r a m e t h y l l e a d . I t might be p o s s i b l e that the compositions of the s o l u t i o n s are d i f f e r e n t . We show t h a t , depending on the composition of the s o l u t i o n , there i s a tremendous i n f l u e n c e on the r a t e of r e d i s t r i b u t i o n r e a c t i o n s of organolead compounds· J . J . ZUCKERMAN ( U n i v e r s i t y of Oklahoma): In some cases you s p e c i f i e d the a c e t a t e ; I take i t that these were s o l u b l e l e a d compounds , and t h a t these engaged i n the r e d i s t r i b u t i o n r e a c t i o n . Did you t r y c o l l o i d a l or i n s o l u b l e lead compounds to see i f they could be m o b i l i z e d by the b i o l o g i c a l species i n these r e a c t i o n s ? CHAU: We t r i e d s e v e r a l i n s o l u b l e compounds, such as l e a d hydroxide , lead c h l o r i d e , and s p a r i n g l y s o l u b l e l e a d carbonate. There was no m e t h y l a t i o n . But even w i t h l e a d n i t r a t e we had d i f f i c u l t y g e t t i n g c o n s i s t e n t r e s u l t s , so I'm not s u r p r i s e d that those i n s o l u b l e compounds d i d n ' t r e a c t . W. P. RIDLEY ( U n i v e r s i t y of Minnesota): I'm i n t e r e s t e d i n your experiments on the methylation of l e a d i n f i s h i n t e s t i n e s . Have you examined the t r a n s p o r t of the methylated a r s e n i c species across the i n t e s t i n a l w a l l of the f i s h ? CHAU: No, we haven't. We used f i s h i n t e s t i n e cut i n t o pieces and mixed i t w i t h an i n o r g a n i c a r s e n i c s o l u t i o n . The b a c t e r i a from the f i s h i n t e s t i n e could transform the arsenate and a r s e n i t e i n t o methyl and dimethyl a r s e n i c compounds.


3.

CHAU AND WONG

Biological Methyfotion

53


K. IRGOLIC (Texas A & M U n i v e r s i t y ) : You showed data on a r s e n i c compounds which you i d e n t i f i e d as d i m e t h y l a r s i n i c and met h y l a r s o n i c a c i d s . As you pointed out, i t i s not n e c e s s a r i l y t r u e t h a t the d i m e t h y l a r s i n e or monomethylarsine you detected need come from these compounds. They could come from an arsenobetaine. I would l i k e t o warn that use of d i m e t h y l a r s i n i c a c i d or methylars o n i c a c i d as a standard i n a n a l y t i c a l procedures does not mean t h a t you have these compounds i n s o l u t i o n . I would l i k e to ask what k i n d of s t r u c t u r e was suggested f o r the v o l a t i l e unknown selenium intermediate i n the methylation of the selenium. WOOD: I n a model system, we were l o o k i n g at the methylation of selenium by dimethylmercury. Under the r i g h t c o n d i t i o n s , you can get methyl t r a n s f e r from dimethylmercury. We i s o l a t e d and c h a r a c t e r i z e d a selenium y l i d as an intermediate. Which i s , i n f a c t , the predominant product of the r e a c t i o n and which i s very r a p i d l y converted to dimethylselenide by b e t a - e l i m i n a t i o n . Dr. Chau had i s o l a t e d something s i m i l a r and I sent him the mass spect r a l data and the mar data. I j u s t learned today when you t a l k e d t h a t these t h i n g s are i d e n t i c a l . CHAU:

Yes, they are i d e n t i c a l .

E. BEVAGE ( U n i v e r s a l O i l P r o d u c t s ) : I s i t your o p i n i o n t h a t the m e t h y l a t i o n of these elements i s given by a wide number o f species of b a c t e r i a or do you f e e l i t i s l i m i t e d t o f a i r l y few? I n o t i c e d you had data on E. c o l i . CHAU: Dr. Wong has i d e n t i f i e d s e v e r a l b a c t e r i a l s p e c i e s , namely Aeromonas and Pseudomonas, very common i n l a k e sediments. They do c a r r y out methylation. I t h i n k we have i d e n t i f i e d f o u r s p e c i e s of b a c t e r i a which could c a r r y out t h i s m e t h y l a t i o n . It is more f a v o r a b l e i n anaerobic s i t u a t i o n s . Sometimes m e t h y l a t i o n occurs w i t h e i t h e r aerobic or anaerobic c o n d i t i o n s as w i t h a r s e n i c . RECEIVED August 22,

1978.


Organometals and Organometalloids - ACS Publications - American

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