In several samples, as shown in Table 1, there was a noticeable increase in chromium concentrations during the postmonsoon period compared to the premonsoon period. In terms of the EPA's MCL for total chromium in drinking water, set at 100 parts per billion (ppb), the results reveal that several samples during the postmonsoon period exceeded this regulatory limit. For instance, Sample A2 exhibited a significant increase from 0.835 ppb to 2174 ppb, and Sample A5 demonstrated an increase from 0.459 ppb to 2391 ppb. In accordance with the Indian Standard IS 10500, which establishes a regulatory value for total chromium in drinking water of 50 parts per billion (ppb) or 50 micrograms per liter (µg/L), the data indicate a breach of the regulatory limit. Both Sample A2 (2174 ppb) and Sample A5 (2391 ppb) had chromium concentrations well above the permissible limit. Notably, during the premonsoon period, Sample K1 exhibited a relatively high concentration of 0.735 ppb, while Sample A3 exhibited a lower concentration of 0.337 ppb. These values are consistent with those of the U.S. Environmental Protection Agency (EPA) Maximum Contaminant Level (MCL) for total chromium in drinking water, which is set at 100 parts per billion (ppb); both Sample K1 (0.735 ppb) and Sample A3 (0.337 ppb) are well below this regulatory limit.
Notably, the postmonsoon samples (Sample A2 and Sample A5) surpassed the IS 10500 limit, indicating a notable increase in chromium concentration due to increased precipitation and mobilization of heavy metals in the environment. The monsoon season may enhance the leaching of chromium and cadmium from geological formations, soil, or other sources, leading to elevated concentrations in water. Therefore, in terms of the EPA's standard, these concentrations are considered within the acceptable range. Similarly, considering the Indian Standard IS 10500, which sets the regulatory value for total chromium in drinking water at 50 parts per billion (ppb) or 50 micrograms per liter (µg/L), both Sample K1 (0.735 ppb) and Sample A3 (0.337 ppb) also meet the regulatory requirement. These concentrations are below the permissible limit established by IS 10500. The observed increases in chromium levels during the postmonsoon period, coupled with the exceedance of both the EPA MCL and the IS 10500 regulatory value, highlight the critical importance of comprehensive actions to address potential environmental contamination. Chromium, often associated with industrial activities such as metal plating and tanning processes, can have adverse effects on ecosystems and human health when present at elevated concentrations. Thus, proactive monitoring, stringent control measures, and effective remediation strategies are crucial for preventing further contamination and safeguarding the quality of drinking water sources. In contrast, the postmonsoon period exhibited a significantly greater standard deviation of 924.188563. This indicates a substantial variation or dispersion in chromium concentrations among the samples during this period, as shown in the graph (Fig. 2). The large standard deviation suggests that the chromium concentrations in the postmonsoon samples were widespread, with some samples exhibiting exceptionally high concentrations. These standard deviation values shed light on the degree of variation in chromium concentrations and provide a measure of the dispersion of the data within each period. The higher standard deviation in the postmonsoon period suggested the possibility of additional sources or factors contributing to the observed variability in chromium levels during this time.
Table 1
Pre- and postmonsoon chromium concentrations
| Latitude, Longitude | Chromium Concentration (premonsoon) (ppb) | Chromium Concentration (postmonsoon) (ppb) | Standard deviation | Cadmium Concentration (premonsoon) (ppb) | Cadmium Concentration (postmonsoon) (ppb) | Standard deviation |
A 1 | 28.60606,77.49602 | 0.753 | 652 | 460.5011699 | 0.097 | 49 | 34.57964292 |
A2 | 28.60369,77.49528 | 0.835 | 2174 | 1536.659708 | 0.156 | 48 | 33.83081684 |
A3 | 28.602069,77.494213 | 0.337 | ND | 0.238294985 | 0.201 | 44 | 30.97056991 |
A4 | 28.59706,77.50084 | 0.456 | 1487 | 1051.145343 | 0.234 | 98 | 69.13100157 |
A5 | 28.59692,77.50186 | 0.459 | 2391 | 1690.367752 | 0.345 | 96 | 67.63829915 |
A6 | 28.59652,77.50506 | .678 | 1675 | 1183.92444 | 0.368 | 97 | 68.32914248 |
S1 | 28.58769,77.51106 | 0.351 | 1845 | 1304.363817 | 0.228 | 99 | 69.84235099 |
S2 | 28.58760,77.58045 | 0.139 | 1945 | 1375.224402 | 0.144 | 104 | 73.43728187 |
S3 | 28.58947,77.51042 | 0.284 | ND | 0.200818326 | 0.223 | 96 | 67.72456618 |
S4 | 28.58741,77.51225 | 0.284 | ND | 0.200818326 | 0.223 | 97 | 68.43167296 |
S5 | 28.58930,77.51334 | 0.384 | 1995 | 1410.406499 | 0.253 | 92 | 64.87492585 |
D1 | 28.61352,77.51456 | 1.202 | 2321 | 1640.344897 | 0.242 | 87 | 61.34717012 |
D2 | 28.61851,77.49194 | 0.17 | 2391 | 1690.572106 | 0.135 | 88 | 62.12993733 |
D3 | 28.614457,77.516773 | 0.235 | 2397 | 1694.768784 | 0.129 | 86 | 60.71996641 |
D4 | 28.61675,77.51715 | 0.175 | 2275 | 1608.544184 | 0.189 | 89 | 62.79886034 |
D5 | 28.62128,77.51763 | 0.235 | 3145 | 2223.684657 | 0.129 | 85 | 60.01285963 |
K1 | 28.60934,77.48806 | 0.735 | 1522 | 1537.044374 | 0.198 | 100 | 70.57067098 |
K2 | 28.61194,77.48878 | 0.291 | 2174 | 1537.044374 | 0.298 | 105 | 74.0354942 |
K3 | 28.61174,77.48894 | 0.713 | ND | 0.504167135 | 0.386 | 121 | 85.28697731 |
K4 | 28.612596,77.492087 | 0.341 | 652 | 460.7924979 | 0.498 | 109 | 76.72249997 |
K5 | 28.60308,77.49164 | 0.291 | 2391 | 1690.486546 | 0.298 | 96 | 67.67153317 |
B1 | 28.61396,77.50195 | 0.377 | 2391 | 1690.425735 | 0.213 | 98 | 69.14585081 |
B2 | 28.61131,77.50140 | 0.69 | 2381 | 1683.133342 | 0.221 | 97 | 68.43308718 |
B3 | 28.61467, 77.50110 | 0.491 | 1304 | 921.7200532 | 0.169 | 100 | 70.59117707 |
B4 | 28.61429, 77.49549 | 0.466 | 1957 | 1383.478459 | 0.154 | 98 | 69.18757011 |
B5 | 28.60352,77.49508 | 0.398 | 1959 | 1384.940756 | 0.147 | 99 | 69.89962664 |
Table 2
Pre- and Postmonsoon Cadmium Levels
Pre-Monsoon Cadmium Levels | Post-Monsoon Cadmium Levels |
Mean: 0.2092 ppb | Mean: 86.04 ppb |
Standard Deviation: 0.1232 ppb | Standard Deviation: 20.24 ppb |
Minimum: 0.097 ppb | Minimum: 44 ppb |
Maximum: 0.498 ppb | Maximum: 100 ppb |
The statistical analysis in Table 2 shows that both the mean and standard deviation of the postmonsoon cadmium levels were greater than those of the premonsoon levels. Additionally, the maximum value of the postmonsoon data exceeded the limit of 3 ppb, indicating potential noncompliance. To further analyze the data, we can compare the measured cadmium levels against the limit of 3 ppb. In the Pre-Monsoon data, all the measured values were below the limit of 3 ppb, indicating compliance with the specified limit. According to the postmonsoon data, the majority of the measured values (24 out of 25) exceeded the limit of 3 ppb, suggesting noncompliance with the specified limit.
The data below summarize the concentrations of chromium and cadmium likely measured in premonsoon samples. There were 26 samples analyzed for each metal, and fortunately, none of the data were missing. On average, the chromium concentration (0.453 mg/L) was greater than the cadmium concentration (0.226 mg/L). There was also more variation in the chromium concentration (standard deviation of 0.250 mg/L) than in the cadmium concentration (standard deviation of 0.093 mg/L). The lowest concentrations were 0.139 mg/L for chromium and 0.097 mg/L for cadmium, while the highest concentrations were 1.202 mg/L and 0.498 mg/L for chromium and cadmium, respectively, as shown in Table 3. Overall, the data suggest that chromium was present at higher levels and with greater variability than cadmium in these premonsoon samples.
Table 3
Comparisons of Chromium and Cadmium Concentrations during the Premonsoon Seasonal
Variable | Observations | Obs. with missing data | Obs. without missing data | Minimum | Maximum | Mean | Std. deviation |
Chromium Concentration (premonsoon) | 26 | 0 | 26 | 0.139 | 1.202 | 0.453 | 0.250 |
Cadmium Concentration (premonsoon) | 26 | 0 | 26 | 0.097 | 0.498 | 0.226 | 0.093 |
A nonparametric Wilcoxon signed-rank test was used to investigate potential differences in the distributions of premonsoon chromium concentration (V) and cadmium concentration (V*) (n = 327). The test statistic (V = 327) and its standardized value (V* = 3.848) indicated a substantial deviation from the expected value (175.500) under the assumption of identical distributions. The calculated variance (V = 1549.875) further supported this observation. Notably, the exact p value could not be computed, but an approximation resulted in a highly significant value (p < 0.000). This outcome suggested that the distributions of these two variables differed significantly, as shown in Fig. 3.
A paired case–control study of human blood samples was conducted after obtaining ethical clearance from Sharda University, Greater Noida. The presence of p16 methylation in the blood is indicated by the formation of a band of approximately 150 bp. As shown in Table 4, 16 of 25 (64%) subjects in the high chromium and cadmium exposure group exhibited p16 hypermethylation. In sharp contrast, only 2 of 25 (8%) subjects in the control group were p16 methylation positive. These results suggest that there is a significant correlation between p16 hypermethylation and the presence of chromium and cadmium in water.
Table 4
Frequency of p16 hypermethylation in the study groups
S.no | Group | p16 positive | p16 negative | Total No. of samples | Standard deviation | P Value |
1 | Chromium and Cadmium Exposure | 16(64%) | 9 | 25 | 0.65064 | .002 |
2 | Control | 2(8%) | 23 | 25 | 0.52599 | .265 |
The results indicate that there are significant differences between the p16-positive and p16-negative samples in both the Cr and Cd exposure groups and the control group. The differences are statistically significant based on the p values provided. The values for the standard deviation and margin of error indicate the variability of the data within each group.
Table 5
Frequency of p16 gene methylation and smoking status in cancer patients and healthy controls.
Gene | Methylation status | Cases (25) | Control(25) | OR | 95% CI | P value |
P16 | M | 9(36%) | 2(8% ) | 1.0737 | .44-.84 | .03 |
The p value of 0.03 is less than the commonly used significance level of 0.05. Methylation of the P16 gene was associated with a significant risk of developing OSCC (Table 5). P16 was methylated in 36% of smokers among the patients. Only 8% of the controls died.
Table 6
Frequency of methylation of the p16 gene and years of drinking groundwater from Greater Noida Villages
S.no | Group | 95% Confidence Interval | t | df | P Value |
1 | P16 Hypermethylation | .70857 | 3.381 | 24 | .002 |
2 | Control | .09712 | -1.141 | 24 | .265 |
Table 6 shows the significant findings concerning P16 hypermethylation in relation to groundwater, with a 95% confidence interval ranging from 0.70857 to 3.381 and a t value of 24, leading to a statistically significant p value of .002. This finding suggested a notable difference in this group compared to some other reference group, suggesting potential implications regarding P16 gene hypermethylation. Conversely, the control group, evidenced by a narrower confidence interval from − 1.141 to 0.09712 and a nonsignificant p value of .265, indicates that any observed variations within this group are likely attributable to random chance rather than a meaningful difference from a reference.