# Health Risk from Toxic Metals in Wild Rice Grown in Copper Mining-Impacted Sediments
## 3 Results and Discussion
### Human Health Risk Assessment
The Cr level in rice seed samples from the Sand Point site was below the detection limit. For Cd, the carcinogenic risk levels were 7.23 \(\times\) 10\({}^{-6}\) and 1.62 \(\times\) 10\({}^{-5}\) from wild rice seeds harvested from Lake Plumbago and Sand Point, respectively. According to USEPA [16] the regulatory values for As, Cr, and Cd are 1 \(\times\) 10\({}^{-6}\) to 1 \(\times\) 10\({}^{-4}\), so the consumption of rice seeds from both locations poses a lifetime cancer risk for As and Cd, whereas, for Cr, only the Lake Plumbago wild rice seeds pose a carcinogenic risk. Exposure to toxic metals, namely As, Cd, and Cr, through diet, poses excess cancer risk in the population. While Cu, Zn, Cr, Pb, and As can cause non-carcinogenic health effects such as liver, kidney, and neurological disorders, chronic exposure to low doses of As, Cr and Cd can pose an excess cancer risk. Exposure to Cr was shown to increase the lifetime risk of various types of cancer, depending on the type of exposure [23]. Chronic dietary exposure to low levels of Cd has been associated with an increased risk of breast cancer [24]. Chronic dietary exposure to As is very well documented and is known to cause numerous health impacts, including dermal, respiratory, cardiovascular, gastrointestinal, reproductive effects, and many types of cancer, including skin, bladder, liver, kidney, etc. [25]. In addition to its dietary and cultural importance, wild rice also has a significant influence over the food web in Keweenaw Bay as a source of food for waterfowl, muskrats, etc. as seen from the results of this study, while the levels of the individual toxic metals  
Figure 4: Hazard Index (HI) values indicate non-carcinogenic health risk due to exposure to toxic elements from the ingestion of wild rice seeds obtained from Lake Plumbago and Sand Point sloughs. \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Carcinogenic Risk (R)** & \\ \hline
**Metals** & **Lake Plumbago** & **Sand Point** \\ \hline As & 4.11 \(\times\) 10\({}^{-4}\) & 2.16 \(\times\) 10\({}^{-4}\) \\ Cr & 4.47 \(\times\) 10\({}^{-5}\) & - \\ Cd & 7.23 \(\times\) 10\({}^{-6}\) & 1.62 \(\times\) 10\({}^{-5}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Excess cancer risk (R) values for As, Cr, and Cd from the ingestion of wild rice grains growing in Lake Plumbago and Sand Point sloughs. in wild rice are low, the HI values indicate that the toxic metals pose a combined non-carcinogenic risk. Arsenic is the exception and stands out as the element that poses the highest non-carcinogenic risk at both locations. Arsenic is known to have the potential to bioaccumulate in white rice, which is grown in standing water under anoxic conditions. This is also true for lake sediments containing wild rice beds. These sediments are known to be anoxic, resulting in As existing mainly as arsenite [As(III)] [26]. Arsenite has higher mobility in plants compared to arsenate [As(V)], which could explain its accumulation in wild rice grains. The carcinogenic risk from three toxic metals, As, Cd, and Cr, was also elevated in the wild rice grains. While we hypothesized that the wild rice from the Sand Point site could pose an elevated health risk, the wild rice from Lake Plumbago, an inland lake not connected to Lake Superior, was not expected to have elevated levels of toxic metals. Interestingly, health risk data indicate that wild rice grains from Lake Plumbago pose a carcinogenic risk from As, Cd, and Cr. In comparison, wild rice grains from Sand Point pose a carcinogenic risk from As alone. There is a serious lack of data regarding the ecological and health risks due to northern wild rice in Michigan.