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Detoxifying Ability of Quinonoid-Enriched Humic Acids with Respect to Copper
Vladimir A. Kholodov1, Natalia A. Kulikova2, Irina V. Perminova
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Dokuchaev Soil Science Institute, Moscow, Russia, vkholod@mail.ru Lomonosov Moscow State University, Moscow, Russia

Catechol, hydroquinone and p-benzoquinone enriched preparations of humic acid (HA) were obtained by modification of HA of brown coal. Modification included phenolformaldehyde condensation of coal HA with catechol, hydroquinone or copolymerization of HA with p-benzoquinone. All modified HA samples did not expose toxicity to plants. Detoxifying ability of humic preparations toward copper was estimated using seedling bioassay. W heat was used as a test plant. Length of 3-day roots was used as a test response. HA detoxifying ability was quantified using toxicological constants of copper binding to HA are normalized to the organic carbon content in HA preparation (KOCtox) according to the following equation:

D=
where CHA is a concentration of HA;

K OC tox в C HA 1 + K OC tox в C

HA

D is a detoxification coefficient calculated as follows: R - Rd +t Ro - Rt D = 1 - d Rd Ro where: R0 ­ root length of control; Rd - root length in the presence of HA; Rt - root length in the presence of copper; Rd+t - root length in the presence of copper and HA. Modified preparations were shown to possess higher detoxifying ability compared to the initial HA. Detoxifying ability of the quinonoid-enriched humic acids was increasing in the following ascending order: native HA < hydroquinone-enriched HA < catechol-enriched HA < p-benzoquinone-enriched HA. Thus, the chemical modification of humic substances is a powerful tool for creating new ecologically-sound sorbents aimed to control heavy metal pollution in the environment. This work has been supported RFBR (grant 10-03-00803-) and Russian Ministry of Science and Education (state contract 16.740.11.0183).

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