Environmental Engineering Reference
In-Depth Information
complexing agents such as humic acids, as shown by Sures and Zimmermann.
(2007). Schäfer et al. (1998) have performed an experiment in which the main
result was a measurable transfer of PGEs from contaminated soil to plants. They
concluded that Pt-, Rh-, and Pd-transfer coefficients are within the range of immo-
bile to moderately mobile elements, such as Cu. The transfer coefficient decreases
from Pd > Pt ≥ Rh, rendering Pd the most available element of this group. Data also
show that there is uptake of the noble metals into different plant structures, in the
following order: root > stem > leaf (Ballach and Wittig 1996; Schäfer et al. 1998;
Messerschmidt et al. 1994).
5.2
Effects on Animals
Recent investigations with zebra mussels (
Dreissena polymorpha
) exposed to
water, containing road dust or ground catalytic converter material, demonstrated
that humic water from a bog lake clearly enhances the biological availability of
particle-bound Pt; nonchlorinated tap water did not have this effect, and Pd showed
the opposite result. No clear trend emerged for Rh. Differences in the effects of
humic matter among the PGEs may be explained by the formation of metal com-
plexes with different fractions of humic substances. The highest metal uptake rates
and highest bioaccumulation plateaus were found for Pd, followed by Pt and Rh
(Zimmermann et al. 2003, 2005; Sures et al. 2001). It was concluded that the uptake
of Pt by the crustaceans
Asellus aquaticus
and
Gammarus pulex
is relatively high,
when compared with other traffic-related heavy metals, or essential metals, such as
zinc (Zn) (Haus et al. 2007). However, Microtox toxicity tests have shown that the
EC
50
(effective concentration of a substance that elicits 50% of a maximum
response) of platinum chloride for the bacterium
Photobacterium phosphoreum
is
25 mg L
−1
, which is much lower than for copper (200 mg L
−1
) (Chen and Morrison
1994). A ranking of 80 metals for toxicity by Wolterbeek and Verburg (2001)
revealed that Pt (II) and Pt (IV) ranked 10th and 11th, respectively [similar to Hg
(mercury) (II) and Pb (lead) (IV)] (Wolterbeek and Verburg 2001; Sutherland
2003). PGEs, at high concentrations, cause water stress, chlorosis, and phytotoxicity
in plants. Pt complex compounds are known to be mutagenic and carcinogenic, and
inorganic Pt complex compounds are mutagenic in bacteria (Gebel et al. 1997;
Sutherland 2003). The order in which PGEs are taken up is similar in exposed
animals and plants: Pd > Pt > Rh. In animals, the liver and kidneys accumulate the
highest levels of PGEs, especially Pd (Ek et al. 2004). Pt toxicity varies with
oxidative state and electron configuration (Roshchin et al. 1984). The least harmful
forms are metallic Pt and its nonsoluble salts (Table 2), although toxic effects are
caused by a small group of Pt compounds that contain active substituents (chloride
substituents are the most reactive). Studies carried out on rats showed that the
amount of Pt retained in the body after 24 hr depended on the metal's chemical
form; the following order was observed: PtCl
4
> Pt(SO
4
)
2
> PtO
2
> Pt (Moore et al.
1975a; Artelt et al. 1999a; Ravindra et al. 2004).
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