# Assessment of Heavy Metal Distributions in Sand Beaches in the Maltese Islands
## 2 Materials and Methods
### Health Risk Assessment  
Long-term human exposure to heavy metals and toxins in the environment leads to various negative health effects. Such heavy metals may enter the human body through inhalation, dermal contact, and ingestion; the latter two are the most relevant to possible toxicity from sand beaches. These health risks are evaluated by several parameters including the Hazard Quotient (HQ) and the Hazard Index (HI), which are dependent on the Average Daily Dose (ADD) and the Reference Dose (RFD) for each heavy metal studied. RFD signifies the reference dose for each heavy metal that an individual is exposed to per day, either by ingestion or dermal contact, throughout his entire life without it causing any harm. ADD values, HQ values, and HI are computed using the equations shown below, with parameters used to compute such values included in Tables 2 and 3, respectively. Adverse non-carcinogenic effects are characterised by values of HQ > 1, while if HQ < 1, concentrations obtained signify no detrimental effects. If the Hazard Index (HI) < 1, the non-carcinogenic adverse effects are assumed to be negligible [20; 21]. \[\text{ADD}_{\text{Ingestion}}=\frac{\text{C}_{\text{s}}\times\text{IR}_{ \text{ingest}}\times\text{EF}\times\text{ED}\times\text{CF}}{\text{BW}\times \text{AT}} \tag{1}\]  
\[\text{ADD}_{\text{dermal}}=\frac{\text{C}_{\text{s}}\times\text{SA}\times \text{AF}\times\text{ABS}\times\text{EF}\times\text{ED}\times\text{CF}}{\text{ BW}\times\text{AT}} \tag{2}\]  
\[\text{HQ}=\frac{\text{ADD}}{\text{RFD}} \tag{3}\]  
\[\text{HI}=\sum_{i=0}^{n}\text{HQ}_{i} \tag{4}\]  
where Cs represents the average heavy metal sample concentration; IRingst represents the heavy metals ingestion rate; EF represents the exposure frequency; ED represents the exposure duration; BW represents the average body weight for adults or children; AT represents the averaging time for carcinogens and non-carcinogens; CF is a unity conversion factor; SA represents the estimated average exposed skin area; AF represents the adherence factor; ABS represents the dermal absorption fraction; HI is the overall toxic risk; and n represents the total number of metals under consideration, as stated in the United States Environmental Protection Agency IRIS (USEPA IRIS) (2011) [21], the United States Environmental Protection Agency _Exposure Factors Handbook_: 2011 Edition [22], and the United States Environmental Protection Agency Update for Chapter 5 of the _Exposure Factors Handbook: Soil and Dust Ingestion_[23], which are referenced by [PERSON] and [PERSON] (2010), [PERSON] et al. (2020), and [PERSON] et al. (2017) [20; 24; 25] and are shown in Table 2. It should be noted that an adjustment on the EF has been taken from the default values used in standard studies, since in this case persons exposed to heavy metal toxicity from sand beaches do not typically spend a full year at the beach. A typical EF of eight-hour days for four months (summer period) in a year has been approximated, as tabulated below. It should also be noted that the values documented in Table 2 for the Exposed Skin Area include the head, 75% of the body trunk, arms, hands, legs, and feet for adults and children using values documented in the United States Environmental Protection Agency _Exposure Factors Handbook_: 2011 Edition [23]. AF values for the whole body of adults and children have been averaged out using values specified for different body parts (similarly mentionedfor the SA), using the Mean Solid Adherence to Skin for children playing in sediments (tidal flats) and for adults during clamming in tidal flats [23]. Cancer Risk (CR) denotes the incremental risk for a human to face cancer over a lifetime due to the exposure to carcinogenic matter. The exposure is approximated equal to a full day for an estimate of 70 years, which represents an approximate full lifetime for a person [30].