PREFACE A r s e n i c is a n e n v i r o n m e n t a l l y u b i q u i t o u s G r o u p V a element. A l t h o u g h it has a m e t a l l i c a l l o t r o p i c f o r m l i k e the t w o h i g h e r G r o u p V a elements,
a n t i m o n y a n d b i s m u t h , arsenic's
s i m i l a r to p h o s p h o r u s .
c h e m i c a l b e h a v i o r is q u i t e
It has f o u r valence states, —3, 0, + 3 ,
and
+5.
A r s i n e a n d methylarsines are characteristic of A s i n the —3 valence state a n d are generally unstable i n air. A r s e n i c m e t a l is f o r m e d b y r e d u c t i o n Downloaded by 80.82.77.83 on January 12, 2018 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/bk-1975-0007.pr001
of arsenic oxides a n d is a glossy b l a c k m a t e r i a l .
A r s e n i c t r i o x i d e is a
p r o d u c t of s m e l t i n g operations, a n d it is the starting m a t e r i a l for synt h e s i z i n g most arsenical c o m p o u n d s .
It is o x i d i z e d c a t a l y t i c a l l y or b y
b a c t e r i a to arsenic p e n t o x i d e or orthoarsenic a c i d ( H A s 0 ) . 3
4
Arsines
a n d arsenites are generally m o r e toxic t h a n arsenates. I n the n a t u r a l e n v i r o n m e n t , most arsenicals d e g r a d e or w e a t h e r to f o r m arsenate, a l t h o u g h u n d e r anaerobic c o n d i t i o n s arsenite m a y f o r m . B i o t r a n s f o r m a t i o n s m a y o c c u r w h i c h result i n v o l a t i l e arsenicals.
These,
i n t u r n , are r e t u r n e d to the l a n d w h e r e soil a d s o r p t i o n , p l a n t u p t a k e , erosion, l e a c h i n g , r e d u c t i o n to arsines, or other processes occur.
This
n a t u r a l arsenic c y c l e reflects a constant s h i f t i n g of arsenic into the various environmental compartments. T h i s s y m p o s i u m was a r r a n g e d because of current c o n c e r n a n d interest i n the q u a l i t y of o u r e n v i r o n m e n t , p a r t i c u l a r l y as it pertains to trace h e a v y metals. W h i l e arsenic is not a h e a v y m e t a l , it is a m e t a l l o i d w h i c h has a l w a y s generated m u c h interest a n d controversy because m a n y of its c o m p o u n d s have toxic properties.
T h i s s y m p o s i u m , then, was i n t e n d e d
to examine the analysis, soil b e h a v i o r , biotransformations, a c c u m u l a t i o n s , c y c l i n g , a n d m o d e l i n g of arsenate a n d arsenical pesticides i n nature. E.
Beltsville,
A.
WOOLSON
Md.
N o v e m b e r 1,
1974
vii
Woolson; Arsenical Pesticides ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
