|
Porter, WP, JW Jaeger and IH Carlson. 1999. Endocrine, immune and behavioral effects of aldicarb (carbamate), atrazine (triazine) and nitrate (fertilizer) mixtures at groundwater concentrations. Toxicology and Industrial Health 15: 133-150. |
||
| Porter et al. experimented with various mixtures of three contaminants commonly found in groundwater in agricultural regions of the United States. They found synergistic effects at levels of contamination within the range often encountered in US water supplies. The effects involved immune, endocrine and behavioral changes. "The data presented here... suggest that some mixtures can have effects that individual chemicals do not have... the data clearly indicate that even when doses are given in drinking water... more biological responses occur in the presence of mixtures of common groundwater contaminants than if the contaminants occur singly." | ||
| Experiments were performed on adult male outbred mice of two species: white mice (Mus musculus) from a laboratory supply company and deer mice (Peromyscus maniculatus) from a colony maintained at the University of Wisconson. Note, therefore, that the effects were not via in utero contamination. This would suggest that developmental studies might find impacts at far lower levels. | ||
| Three chemicals were used: aldicarb, atrazine and nitrate. Each chemical was tested at two levels (low and high), all within ranges found in Wisconsin groundwater. The high doses used for aldicarb, atrazine and nitrate were 10 parts per billion, 10 ppb and 28 parts per million, respectively. These "high doses" were slightly above the maximum contaminant level for each chemical. | ||
|
"One notable result for this 5-year study is that the trend of our results for individual pesticides agrees with the results of standard toxicological testing protocols used for pesticide product registration. Namely, at current groundwater concentrations there is little or no biological affect." [note: recall these experiments were on adult males, not fetuses in utero.] "There were exceptions to this, however, namely the effect of aldicarb on T4 and PFC (plaque forming cell assay) and the effect of atrazine on PFC." "A second notable result in this study is that effects appear frequently for mixtures, and the level of statistical confidence often increases in comparison to the effects of individual pesticides. Of special significance are the effects that appear when nitrates co-occur with individual pesticides. We saw effects on aggression... body mass...free thyroid index...and on plaque forming." |
||
| Porter et al. comment on the variability of results in their experiments. "Significant single chemical effects and significant interactions occur in some experiments, but not in others. A number of unreplicated factors in the experiments could account for these differences. These include species differences (Peromyscus vs. Mus), exposure time differences, and seasonal differences. Data analysis suggests that seasonal differences may be important." [note... this would not be surprising given that the endocrine system has pronounced annual cycles related to, among many things, the timing of the breeding season.] | ||
| "The induction of thyroid hormone changes by the low-level mixtures we used in this study raises two concerns. One concern is for postnatal individuals. In hyperthyroidism, elevated thyroid levels have been associated with increased irritability and quickness to anger (Whybrow 1991a). Elevated irritability can affect the ability to concentrate and to learn (Boyd et al. 1990). In hypothyroidism, depressed thyroid levels have been associated with lower motivation to learn or to work at full capacity (Whybrow, 1991b). Thyroid hormones are also critical for fetal brain development (Porterfield and Hendrich, 1993; Porterfield and Stein, 1994; Hendrich and Porterfield 1996), which could determine an individual's disposition in adulthood." | ||
| Porter et al. also comment on the shortcomings in testing protocols currently in use to guide regulatory decisions. More... |