The growing demand for enhanced food productivity to meet the needs of the global population has led farmers to use sophisticated agricultural technology in which pesticides play a crucial role. Pesticide use has a positive and dramatic impact on agricultural production through protection of crops against insects, pests, and disease, but every effort must be made to ensure that application is safe and, more importantly, to assure safety for human and environmental health. Since our initial review (1), global usage of pesticides has increased and knowledge regarding the biological significance of bound pesticide residues has expanded. The fact that more reports are appearing in the literature signifies an increased awareness of the presence of bound pesticide residues and indicates that a greater number of scientists are attempting to establish the potential toxicologic consequences of this pesticides residue fraction. Rico (2), in a review in 1990, concluded that covalently bound residues in edible animal tissues were not carcinogenic, were not readily bioavailable, and hence produced little, if any, adverse effects. Whether this conclusion is applicable to the presence and consequences of bound pesticide residues in plants and food commodities remains unanswered. Thus, the aim of this updated review is not simply to list studies on bioavailability of bound pesticide residues in grains subsequent to the review in 1992 (1) but also to establish the toxicological impact of this chemical fraction on health.

The l i t e r a t u r e p e r t a i n i n g t o adsorption o f p e s t i c i d e by humic substances has been reviewed, R e s u l t s o f various i n v e s t ig a t i o n s and mechanisms f o r p e s t i c i d e a d s o r p t i o n a r e discussed, The e f f e c t s o f such f a c t o r s as temperature and pH, and t h e techniques f o r t h e s t u d y o f p e s t i c i d e a d s o r p t i o n by humic substances a r e o u t l i n e d . 11. INTRODUCTION Humic substances a r e . t h e p r i n c i p a l organic components o f -80Xl.s and'waters. and have t h e a b i l i t y . t o form stable water-s'oluble and wateri n s o l u b l e s a l t s and complexes with inorganic and organic compounds. They a r e a c i d i c dark colored, p a r t i a l l y aromatic, chemically complex materials o f molecular weights ranging from a few hundred t o s e v e r a l thousand, Based on t h e i r s o l u b i l i t i e s ,humic substances a r e p a r t i t i o n e d i n t o t h r e e main f r a c t this work may be reproduced or ytilired in ony form or by any means, electronic o r mechanical, including xerography, phofocopying, rnicrofifrn, and recording, or by any information storage and retrieval system, without the written permission of the publisher.