In classical toxicology, speciation of carbon is taken for granted and the carbon compounds responsible for toxicity are always described with the appropriate chemical nomenclature. By contrast, speciation of other elements is largely ignored and elements other than carbon are often condemned as toxic because of evidence relating toxicity to only a few of the chemical species in which they occur.
As an
example, the element arsenic is often taken as a synonym for poison, while the
arsenic compounds present in fish and other seafood are actually as harmless as
table salt:
| CHEMICAL
SPECIES | DL50 (mg/kg)
|
Arsenite
(As(III))
| 14
|
Arsenate
(As(V))
| 20
|
| Arsine
(AsH3) | 3 |
| Monomethylarsonic
Acid (MMA) | 700 - 1800 |
Dimethylarsinic
Acid (DMA)
| 700 - 2600 |
Arsenocholine
| > 10000 |
| Arsenobetaine | > 10000 |
DL50
rat: concentration leading to the death of 50 % of a rat population
Since the
physical, chemical and biological characteristics of a chemical substance
depend primarily on its molecular structure and not on one of its elemental
constituents, so does its toxicity.
As an
example let us discuss the toxicity of organotin compounds:

As has been
shown by Luedke et al., 1991, the toxicity of di- and
tri-organotin compounds (chlorides) depends on the target organism and is a
function of the molecular volume of the compound (and not of the inclusion of a "toxic element" tin in the compound !).
The
toxicity of often called “toxic trace
elements” depends on their speciation and concentration not only in a quantitative
way but also in a qualitative way.
Some examples:
- Cr(III) is
considered to be essential while Cr(VI)
is cancerogen
- Inorganic
As(III) compounds are cancerogen while
Arsenobetaine is essential non-toxic
- Inorganic
tin compounds are discussed asbeing
essential for plants and some animals but
tributyltin (TBT) is an endocrine discuptor
The chemical species of a metal can effect its toxicokinetics by influencing its
- absorption
- distribution
- biotransformation
- elimination.
It is
therefore essential that toxicological studies should always consider the species
rather than the elemental constituent in order to create meaningful data. With
respect to risk assessment and legislation it becomes more and more clear that failure to consider properly
chemical speciation of elements other than carbon can lead to poor use of our
resources. Laws and regulations based on simple elemental analysis may wrongly
condemn environmental media or products as toxic and prevent the use of
important resources.
Related Resources
The Metal Speciation Toxicokinetics Database
EVISA Link Database: Toxicity of Elemental Species
Further Reading
K.A. Biedermann, J.R. Landolph, Role of valency state and solubility of chromium compounds on induction of cytotoxicity, mutagenesis, and anchorage independence in diploid human fibroplasts, Cancer Res., 50/24 (1990) 7835-7842.

E. Luedke, E. Lucero, G. Eng,
Molecular volume as a predictor of organotin biotoxicity, Main Group Metal Chemistry, 14 (1991) 59

S.B. Jonnalagadda, P.V. Rao,
Toxicity, bioavailability and metal speciation, Comp. Biochem. Physiol. C, 106/3 (1993) 585-595.

S.D. Kim, H. Ma, H.E. Allen, D.K. Cha,
Influence of dissolved organic matter on the toxicity of copper to Ceriodaphnia dubia: effect of complexation kinetics, Environ. Toxicol. Chem., 18 (1999) 2433-2437.
DOI: 10.1897/1551-5028(1999)018<2433:IODOMO>2.3.CO;2
J.H. Duffus,
Chemical speciation terminology: chromium chemistry and cancer, Mineral. Mag. (London), 69/5 (2005) 557-562.
doi: 10.1180/0026461056950270
K.F. Akter, G. Owens, D.E. Davey, R. Naidu,
Arsenic speciation and toxicity in biological systems, Rev. Environ. Contam. Toxicol., 184 (2005) 97-149.
doi: 10.1007/0-387-27565-7_3
P. Apostoli, R. Cornelis, J. Duffus, P. Hoet, D. Lison, D. Templeton,
Elemental Speciation in Human Health Risk Assessment, WHO,
Environmental Health Criteria #234 (2006)
Richard J. Reeder, Martin A. A. Schoonen, Antonio Lanzirotti,
Metal Speciation and Its Role in Bioaccessibility and Bioavailability, Rev. Mineral. Geochem., 64/1 (2006) 59-113.
DOI: 10.2138/rmg.2006.64.3
last time modified: August, 30, 2008