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The San Juan-Taxco River system is situated in the Taxco mining district, which is a well-known international producer of silver, jewelry and precious metal handicrafts. The population and biota in the area have been affected by inappropriate disposal of anthropogenic activities that pollute the hydric resources and threaten their health and sustainability, since the inhabitants use the groundwater and river water for human consumption, domestic water supply and irrigation. This study was conducted to assess the pollution in the river system, human health implications and ecological risk in the aquatic environment (groundwater, surface water and superficial sediment). This evaluation was done on the base of hydrochemical, textural, mineralogical and geochemical analysis supported by calculation of human health risk using chronic daily intake (CDI), hazard quotient (HQ) and hazard index (HI) with environmental and geochemical indices for ecological risk evaluation. The health risk assessment indicated increasing non-health carcinogenic risk to the exposed population to the river water and dug wells (HI > 1), and thus, these resources are not recommended for human consumption, domestic activities and prolonged ingestion. The results demonstrated a high degree of pollution due to toxic elements and geochemical indices. The Pollution Load Index indicated potential risk that will cause harmful biological effects in the riverine environment.
Providing feedback to preservice teachers about their teaching style is an important component of most performance-based teacher education models. In these models it is assumed that if preservice teachers are provided a critique of their ability to perform a certain teaching behavior in a specific microteaching setting, then the teachers will be able to improve their ability to perform that behavior in subsequent teaching assignments. Interest has been shown by a number of researchers about whether the source of feedback criticism (i.e., feedback from self, peer, pupil, or supervisor) has an effect on the preservice teachers' ability to perform the teaching behavior of interest. Research results relative to this issue have been conflicting and no definitive conclusions about the effect of feedback source have been made. The present article explores whether the feedback source (i.e., self, peer, or supervisor) has any effect on the attitudes and on the ability of preservice teachers to employ three specific teacher behaviors.The source of feedback to the preservice teacher constituted the independent variable for the study. Subjects received feedback criticism about their lesson either from themselves, a peer, or a supervisor. A fourth group of subjects served as a control group and observed pupil behaviors which were not related to the teaching behaviors of interest.Five dependent variables were chosen as representative of important behaviors and attitudes of preservice teachers. The first variable was the proportion of high inquiry teacher questions to all teacher questions. This was considered important since Ladd and Andersen[ 13 and others[2, 31 had shown or claimed a relationship between frequency of high inquiry teacher questions and pupil performance. The second dependent variable was the proportion of teacher probing questions to all teacher questions. The value of asking probing questions, which cause students to clarify, extend, focus, justify, or apply their previous responses, has been claimed and included as a part of the inquiry teaching method by several authors (e.g., Renner et a1.[4]). The third dependent variable, wait time species two, is defined as the period of silence following a student's response and preceding a teacher's or another student's verbalization, and its value has been shown by Rowe [S] . The final dependent variables were the attitude of preservice teachers toward the way in which feedback was given to them and their attitude toward science teaching.Science Education 62(2): 209-214 (1978) (2):81-94 (1974).
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