Radioactive Materials - An Overview

Introduction:

The emergence of radioactive isotopes has become a boon to modern healthcare as it can aid in the early detection of diseases followed by timely and effective management of medical conditions. However, safe disposal of radioactive isotopes should be given equal importance as improper disposal leads to unwanted environmental exposure. Patients and the working staff of healthcare facilities are at increased risk of contracting the health hazards. Radioactive waste management has been initiated to ensure that the exposure does not cross the safety limits and to protect individuals and the environment from unnecessary exposure to radioactive materials.

What Are the Most Commonly Used Diagnostic Radioisotopes?

The radioisotopes that are commonly used for diagnostic purposes in hospitals are technetium-99m (Tc-99m), Iodine-131 (I-131), Iodine-125 (I-125), Iodine-123(I-123), Fluorine-18 (F-18), Tritium (H-3) and Carbon-14 (C-14).

Why Should Radioactive Isotopes Be Disposed of According to the Hospital Waste Management?

• The Department of Nuclear Medicine is responsible for the major amount of radioactive waste generated in the hospital.

• The radioactive waste generated is usually present in liquid form, whereas a small number of them are solid and gaseous.

• Solid wastes like syringes, needles, cotton swabs, vials, contaminated gloves, and absorbent materials contain radioactive traces.

• The patients who are administered high doses of radioisotope I to 131 contain radioactive waste in their clothing and the utensils they use lead to unwanted environmental exposures.

• Hence, it is the responsibility of every health institution to recognize the wastes generated from nuclear medicine and ensure the safe disposal of radioactive wastes without causing harm to the surroundings.

• The main objective of radioactive waste management is to ensure the exposure caused by radioactive radiation should not cross the safety levels, thereby protecting the health of the public, radiation workers, and the environment.

• The short-term and long-term effects of ionizing radiation on public and environmental health are prevented by keeping track of radiation exposure.

What Are the Fundamental Principles of Radioactive Waste Management?

The basic principles of radioactive waste management include:

• Judicious Practice: Radioisotopes are used as diagnostic aids only when it is required, and the benefits are more than the risks in managing a case.

• Optimal Utilization: Keeping the magnitude of the dose for every individual and limiting the exposure of radiation to others as low as reasonably achievable (ALARA principle).

• Regular Evaluation: Periodic monitoring of radiation workers, hospital surroundings, and regular monitoring of the quality of the radiation equipment is done to ensure the radiation safety standards.

• Recruiting RSO (Radiation Safety Officer): Every hospital must recruit a radiation safety officer who is responsible for radiation safety and radioactive waste management.

How Are Radioactive Wastes Classified?

Radioactive wastes are classified as follows:

According to Level of Activity:

• High-Level Waste: Usually generated from the nuclear industry and nuclear reactors.

• Medium-Level Waste: Some hospital-generated wastes.

• Low-Level Waste: Usually generated from hospitals.

According to the Form:

• Solid waste.

• Liquid waste.

• Gaseous waste.

According to Half-Life:

• Longer half-life waste, having a half-life of more than a month.

• Shorter half-life waste, having a half-life of less than a month.

How Is the Waste Management of the Radioactive Material Carried Out in Healthcare Facilities?

Radioactive waste management takes place in two steps:

Collection:

• The first and foremost step in radioactive waste disposal is the identification and grouping of the waste and disposal into respective containers at the end of the day.

• Solid radioactive wastes are discarded into foot-operated waste disposal bins with disposable polythene lining, and liquid wastes are put into polythene carboys.

• Radioactive wastes should never be collected in glassware containers.

• The disposal bin into which the radioactive wastes are discarded should be properly labeled; the activity level details need to be mentioned, which in turn decides the method of disposal.

• Only combustible radioactive wastes can be disposed of through incineration in hospitals, and permission to do so should be sought before the waste disposal.

• Disposal of two different radioisotopes with different half-lives, like Tc-99m and I-131, should be carried out in separate bins.

• The bin used for collecting the waste should be properly labeled with all the details, including the name, activity level, and date of monitoring.

Dilute and Disperse:

• Low-activity solid wastes like vials, syringes, cotton swabs, and tissue papers can be discarded as other hospital-based wastes only if the activity level does not cross 1.35 microcuries and the overall concentration does not exceed 135 microcuries / m3 (5MBq / m3).

• Likewise, liquid radioactive waste material can be discarded through a sanitary sewage system by flushing it with water adequately. However, the disposal of liquid waste should not exceed the safety limits.

Delay and Decay:

• This method involves storing the radioactive wastes until they decay and are then disposed of.

• Medium-activity radioactive waste and the ones whose half-life is less than a month are stored in a room with lead shielding. The thickness of the lead shielding should be adequate to prevent radiation leakage.

• The storage room should be provided with adequate ventilation and exhaust facilities, and the wastes should be eliminated through a duct ending in a rooftop exit.

• The radioactive wastes are stored to decay to a minimum of 10 half-lives so that around 0.1 % of the initial activity of the radioactive waste is retained.

• The waste is checked for activity level and disposed of, like any other solid or liquid waste, if it is of low activity level and does not cause any harm.

• The majority of the low and medium-level radioactive hospital wastes are disposed of through this method as they have shorter half-lives, permitting delay and decay of the waste disposal.

Concentrate & Contain:

• Radioactive wastes of higher activity levels and long half-lives are chosen for disposal through this method.

• The delay and decay method seems to be irrational for disposing of high-activity radioactive wastes due to the lack of availability of space, and the wastes have longer half-lives and demand long storage time.

• This method involves the disposal of wastes in containers designed for the same with appropriate labeling and buried in respected burial sites under the supervision of the allotted authority.

• Usually, hospital wastes are of low and medium activity levels, and hence, most of them are disposed of through the delay and decay method. Hence, the concentrate and contain method is rarely used as it involves environmental concerns.

Incineration:

• The incineration method is used to dispose of the insoluble liquid waste that is generated from liquid scintillation.

• The incineration method works by lowering the quantity of the waste generated and concentrates a small amount of ash, which is further disposed of.

• However, the incinerators release the radiation into the atmosphere. Hence, incinerations should be carried out under controlled conditions and in specific places. The ash generated is disposed of separately as solid waste.

• As the delay and decay and incineration methods cause environmental concerns and public health risks, these methods are rarely preferred for disposing of radioactive wastes.

Conclusion:

Modern healthcare facilities tend to depend on recent diagnostic advances involving radioisotopes, which are essential for the early detection of tumors and other health conditions and play an important role in improving the overall prognosis of the treatment. This has led to an increased output of radioactive wastes from the hospitals, which has to be discarded safely without burdening the environment and public health. The International Atomic Energy Agency (IAEA) and national agencies like the Atomic Energy Regulatory Board (AERB) of India have provided regulations to discard radioactive wastes safely. These agencies strive to promote the safe disposal of radioactive wastes to prevent the ill effects of radioactive wastes on the community.