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